Projections from the 'cingular' vocalization area in the squirrel monkey.

In 5 squirrel monkeys the anatomical projections from the 'cingular' vocalization area were studied by the autoradiographic tracing technique. The 'cingular' vocalization area lies around the sulcus cinguli at the level of the genu of the corpus callosum; its electrical stimulation yields purring and cackling calls. The following efferent connections were found: corticocortical fibers could be traced into the orbital cortex (areas 10 and 11), dorsomedial frontal cortex (areas 9, 8 and 6), limbic cortex (areas 25, 24 and 23), Broca's area (area 44), frontal operculum (area 50), insula (areas 13 and 14), and auditory association cortex (area 22). Subcortical terminal fields within the telencephalon were found in the nucleus caudatus, putamen, claustrum, globus pallidus, olfactory tubercle, preoptic region and nucleus centralis and basolateralis amygdalae. Fibers reached most of these structures along different trajectories. In the diencephalon terminal fields lay in the dorsal hypothalamus, the subthalamus, lateral habenular nucleus, and the following thalamic nuclei: nucleus reticularis, ventralis anterior, centralis medialis, centralis superior lateralis, centralis inferior, submedius, medialis dorsalis and centrum medianum. In the midbrain, the periaqueductal gray was the only projection area, extending into the parabrachial nuclei at the pontomesencephalic transition. The most caudal terminal field was found in the medial pontine gray. No terminals were detected in the nucleus ambiguus, nucleus n. hypoglossi or in any other cranial motor nucleus involved in phonation processes. A comparison of this projection system with the whole of structures producing vocalization when electrically stimulated yielded only partial overlap. Not all vocalization areas lie within the 'cingular' projection system, and inversely, not the whole projection system yielded vocalization. Overlap took place in the anterior limbic cortex, preoptic region, central amygdaloid nucleus, midline thalamus, dorsal hypothalamus, periaqueductal gray and parabrachial nuclei. These structures are considered to compose a functionally coherent vocalization system. The projections into Broca's area, nucleus ventralis anterior thalami, frontoopercular cortex within the lateral fissure, pontine nuclei and superior temporal gyrus are discussed in their possible relationship to vocalization processes.     

Afferent fibers to the cingular vocalization region in the squirrel monkey

Three squirrel monkeys (Saimiri sciureus) received horseradish peroxidase injections in the anterior cingulate cortex at the level of the genu of the corpus callosum, a region yielding vocalization when electrically stimulated. Retrogradely labeled neurons were found at the cortical level within the dorsomedial and lateral prefrontal cortex (areas 9 and 10), orbital cortex (area 11), premotor cortex (areas 44, 6b, and 8), frontoparietal operculum, insula, cortex of the superior temporal sulcus, piriform cortex, subiculum, posterior cingulate, and retrosplenial cortex. Subcortical telencephalic projections came from the the claustrum, diagonal band of Broca, nucleus basalis Meynert, nuclei basalis lateralis and accessorius amygdalae, and cells at the periphery of globus pallidus. Diencephalic structures projecting to the anterior cingulate cortex were the thalamic nuclei anterior medialis, anterior ventralis, ventralis anterior, ventralis lateralis pars medialis, medialis dorsalis, pulvinaris medialis, centralis superior lateralis and limitans; the intralaminar nuclei paracentralis, centralis lateralis and parafascicularis; and the midline nuclei periventricularis, parataenialis, centralis superior, centralis inferior, centralis medialis, and reuniens. In the hypothalamus, projections came from the periventricular, lateral and posterior part, as well as the supramamillary nucleus. Midbrain afferent fibers came from the ventral tegmental area of Tsai, medial substantia nigra, reticular formation, area praerubralis, nucleus peripeduncularis, and periaqueductal gray. The most posterior labeled neurons were found in the locus ceruleus, dorsal tegmental nucleus of Gudden, nucleus annularis, nucleus centralis superior Bechterew, nucleus dorsalis raphae and the most dorsomedial part of the nucleus reticularis tegmenti pontis. Some of those projections have functional significance in the light of the hypothesis that the cingular cortex is involved in the volitional control of emotional reactions on the one hand and the influence of primary emotional reactions on intentional behavior on the other.     

Left anterior temporal cortex actively engages in speech perception: A direct cortical stimulation study

Recent neuroimaging studies proposed the importance of the anterior auditory pathway for speech comprehension. Its clinical significance is implicated by semantic dementia or pure word deafness. Neurodegenerative or cerebrovascular nature, however, precluded precise localization of the cortex responsible for speech perception. Electrical cortical stimulation could delineate such localization by producing transient, functional impairment. We investigated engagement of the left anterior temporal cortex in speech perception by means of direct electrical cortical stimulation. Subjects were two partial epilepsy patients, who underwent direct cortical stimulation as a part of invasive presurgical evaluations. Stimulus sites were coregistered to presurgical 3D-MRI, and then to MNI standard space for anatomical localization. Separate from the posterior temporal language area, electrical cortical stimulation revealed a well-restricted language area in the anterior part of the superior temporal sulcus and gyrus (aSTS/STG) in both patients. Auditory sentence comprehension was impaired upon electrical stimulation of aSTS/STG. In one patient, additional investigation revealed that the functional impairment was restricted to auditory sentence comprehension with preserved visual sentence comprehension and perception of music and environmental sounds. Both patients reported that they could hear the voice but not understand the sentence well (e.g., heard as a series of meaningless utterance). The standard coordinates of this restricted area at left aSTS/STG well corresponded with the coordinates of speech perception reported in neuroimaging activation studies in healthy subjects. The present combined anatomo-functional case study, for the first time, demonstrated that aSTS/STG in the language dominant hemisphere actively engages in speech perception.     

Direct and indirect pathways from the amygdala to the frontal lobe in rhesus monkeys

To elucidate the anatomical relationships between the frontal association cortex and the limbic system in primates, projections from the amygdala to frontal cortex were studied in the rhesus monkey using retrograde and anterograde tracing methods. Following injections of horseradish peroxidase (HRP) into the orbital prefrontal cortex, the gyrus rectus, the superior frontal gyrus, and the anterior cingulate gyrus of the frontal lobe, labeled neurons were found in the basolateral, basomedial, or basal accessory nuclei of the amygdala. None of these nuclei contained labeled neurons following HRP injections into the principal sulcus or the lateral inferior convexity of the frontal lobe. This selective distribution of amygdala connections was confirmed by injection tritiated amino acids into the amygdala. Silver grains were present only over the orbital cortex and gyrus rectus on the ventral surface of the frontal lobe and over the superior prefrontal gyrus and anterior cingulate gyrus on the medial wall of the hemisphere, while the dorsolateral prefrontal cortex was free of radioactivity. The isotope injection of the amygdala also revealed a projection to the magnocellular moiety of the mediodorsal nucleus (MDmc) which is known to innervate the same ventromedial regions of the frontal lobe that receive direct connections from the amygdala. Although MDmc and amygdala project to the same cortical regions, their terminal fields are different. The direct amygdala input terminates in layer 1 in orbital cortex and gyrus rectus and layer 2 in the dorsomedial cortex and cingulate gyrus, while the thalamic input is primarily to layer 3 and, in some areas, also the superficial half of layer 1. These findings indicate that the frontal lobe of rhesus monkeys can be subdivided into two separable cortical regions: 1) A ventromedial region including the anterior cingulate gyrus which receives both direct (amygdalo-cortical) and indirect (amygdalo-thalamo-cortical) input from the amygdala; and 2) a dorsolateral frontal region which is essentially devoid of either direct or indirect amygdalofugal axons. On the basis of its selective relationship with the amygdala, the ventromedial region may be considered the "limbic" portion of the frontal association cortex.     

Hearing suppression induced by electrical stimulation of human auditory cortex

In the course of performing electrical stimulation functional mapping (ESFM) in neurosurgery patients, we identified three subjects who experienced hearing suppression during stimulation of sites within the superior temporal gyrus (STG). One of these patients had long standing tinnitus that affected both ears. In all subjects, auditory event related potentials (ERPs) were recorded from chronically implanted intracranial electrodes and the results were used to localize auditory cortical fields within the STG. Hearing suppression sites were identified within anterior lateral Heschl's gyrus (HG) and posterior lateral STG, in what may be auditory belt and parabelt fields. Cortical stimulation suppressed hearing in both ears, which persisted beyond the period of electrical stimulation. Subjects experienced other stimulation-evoked perceptions at some of these same sites, including symptoms of vestibular activation and alteration of audio-visual speech processing. In contrast, stimulation of presumed core auditory cortex within posterior medial HG evoked sound perceptions, or in one case an increase in tinnitus intensity, that affected the contralateral ear and did not persist beyond the period of stimulation. The current results confirm a rarely reported experimental observation, and correlate the cortical sites associated with hearing suppression with physiologically identified auditory cortical fields.     

Overlapping and nonoverlapping cortical projections to cortex of the superior temporal sulcus in the rhesus monkey: Double anterograde tracer studies

To examine how fibers from functionally distinct cortical zones interrelate within their target areas of the superior temporal sulcus (STS) in the rhesus monkey, separate anterograde tracers were injected in two different regions of the same hemisphere known to project to the STS. Paired injections were placed in dorsal prearcuate cortex and the caudal inferior parietal lobule (IPL), interconnected regions that are part of a hypothesized distributed network concerned with visuospatial analysis or directed attention; in a presumed auditory region of the superior temporal gyrus (STG) and in extrastriate visual cortex, the caudal IPL and lower rim of the intraparietal sulcus; and in dorsal prearcuate cortex and the STG. Overlapping and nonoverlapping projections were then examined in STS visual and polysensory areas. Prefrontal and parietal fibers directly overlapped extensively in area MST and all subdivisions of presumed polysensory cortex (areas TPOc, TPOi, and TPOr), although nonoverlapping connections were also found. Although STG and IPL fibers targeted all TPO subdivisions, connections were to nonoverlapping, but often adjacent, columns. Paired prefrontal and STG injections revealed largely nonoverlapping vertical columns of connections but substantial overlap within layers VI and I of areas TPOc and TPOi. The findings suggest that area TPO contains differently connected modules that may maintain at least initial segregation of visual versus auditory inputs. Other modules within area TPO receive directly converging input from the posterior parietal and the prefrontal cortices and may participate in a distributed cortical network concerned with visuospatial functions. © 1996 Wiley-Liss, Inc.     

Multiple cortical targets of one thalamic nucleus: the projections of the ventral medial nucleus in the cat studied with retrograde tracers

The organization of the cortical projections of the ventral medial thalamic nucleus (VM) was studied in the cat with retrograde tracers. The extent of the VM-cortical projections was first investigated with horseradish peroxidase injected in different cortical fields. The results obtained in the experiments indicated that the main target of VM efferents is represented by a large territory anterior to the cruciate sulcus involving area 6 and the gyrus proreus and extending into the anterior part of the medial cortical surface. The afferents to these precruciate fields arise from throughout the VM. In addition, the lateral third of VM projects upon the lateral precruciate cortex that is coextensive with the precruciate part of area 4, whereas VM efferents do not extend into the posterior sigmoid gyrus. A second major target of VM efferents is represented by the insular cortex in the anterior sylvian gyrus. VM projections also reach the prepyriform cortex and the cingulate gyrus. An anteroposterior decrease of density was found in the VM-cingulate projections. Sparse VM projections reach the temporal cortex, the adjacent posterior sylvian and ectosylvian fields, and the anterior ectosylvian gyrus. No VM projections were found either upon the visual areas 17 and 18 or upon the primary auditory cortex. The interrelations between some VM-cortical cell populations and their divergent collateralization were studied by using double retrograde labeling with fluorescent tracers. The results of these experiments demonstrated that a relatively high number (at least 20%) of VM cells projecting to the insula are also connected to the precruciate fields by means of axon collaterals. This finding indicates that VM is a highly collateralized structure of the cat's thalamus. Very few branched cells were found in the other combinations of cortical fields here examined (precruciate vs. posterior sylvian fields, lateral precruciate vs. proreal cortex, anterior vs. posterior cingulate fields). Altogether these data indicate that VM branched cells preferentially interconnect the two main cortical targets of the nucleus, i.e., precruciate and insular fields. The results of the present study are discussed in regard to the literature on the VM projections in the rat and the previously available data in the cat, to the afferent VM organization in the cat, to the relationships between VM and the nucleus submedius, and to the anatomical and functional role of VM in relation to the so-called "nonspecific" thalamocortical system.     

Parietal,temporal, and occipita projections to cortex of the superior temporal sulcus in the rhesus monkey: A retrograde tracer study

The afferent cortical connections of individual cytoarchitectonic areas within the superior temporal sucus (STS) of the rhesus monkey were studied by retrograde tracer techniques, including double tracer experiments. Rostral superior temporal polysensory (STP) cortex (area TPO-1) receives input from the rostral superior temporal gyrus (STG), cortex of the circular sulcus, and parahippocampal gyrus (PHG) (areas 35, TF, and TL). Mid-STP cortex (areas TPO-2 and -3) has input from the mid-STG, cortex of the mid-circular sulcus, caudal inferior parietal lodule (IPL), cingulate gyrus (areas, 23, 24, retrosplenial cortex), and mid-PHG (areas 28, TF, TH, and TL). Caudal STP cortex (area TPO-4) has afferent connections with the caudal STG, cortex of the cauda insula and caudal circular sulcus, caudal IPL, lower bank of the intraparietal sulcus (IPS), medial parietal lobe, cingulate gyrus, and mid- and caudal PHG (areas TF, TH, TL; prostriate area). The most rostral cortex of the lower bank of the STS (areasTEa and TEm), a presumed visual association area, receives input from the rostal inferotemporal (IT) region; more cauda portions of areas TEa and TEm have afferent connections with the caudal IT region, PHG, preoccipital gyrus, and cortex of the lower bank of the IPS. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Mapping hemispheric asymmetries of the macaque cerebral cortex during early brain development

Studying cortical hemispheric asymmetries during the dynamic early postnatal stages in macaque monkeys (with close phylogenetic relationship to humans) would increase our limited understanding on the possible origins, developmental trajectories, and evolutional mechanisms of brain asymmetries in nonhuman primates, but remains a blind spot to the community. Via cortical surface‐based morphometry, we comprehensively analyze hemispheric structural asymmetries in 134 longitudinal MRI scans from birth to 20 months of age from 32 healthy macaque monkeys. We reveal that most clusters of hemispheric asymmetries of cortical properties, such as surface area, cortical thickness, sulcal depth, and vertex positions, expand in the first 4 months of life, and evolve only moderately thereafter. Prominent hemispheric asymmetries are found at the inferior frontal gyrus, precentral gyrus, posterior temporal cortex, superior temporal gyrus (STG), superior temporal sulcus (STS), and cingulate cortex. Specifically, the left planum temporale and left STG consistently have larger area and thicker cortices than those on the right hemisphere, while the right STS, right cingulate cortex, and right anterior insula are consistently deeper than the left ones, partially consistent with the findings in human infants and adults. Our results thus provide a valuable reference in studying early brain development and evolution.     

Auditory cortex on the human posterior superior temporal gyrus

The human superior temporal cortex plays a critical role in hearing, speech, and language, yet its functional organization is poorly understood. Evoked potentials (EPs) to auditory click-train stimulation presented binaurally were recorded chronically from penetrating electrodes implanted in Heschl's gyrus (HG), from pial-surface electrodes placed on the lateral superior temporal gyrus (STG), or from both simultaneously, in awake humans undergoing surgery for medically intractable epilepsy. The distribution of averaged EPs was restricted to a relatively small area on the lateral surface of the posterior STG. In several cases, there were multiple foci of high amplitude EPs lying along this acoustically active portion of STG. EPs recorded simultaneously from HG and STG differed in their sensitivities to general anesthesia and to changes in rate of stimulus presentation. Results indicate that the acoustically active region on the STG is a separate auditory area, functionally distinct from the HG auditory field(s). We refer to this acoustically sensitive area of the STG as the posterior lateral superior temporal area (PLST). Electrical stimulation of HG resulted in short-latency EPs in an area that overlaps PLST, indicating that PLST receives a corticocortical input, either directly or indirectly, from HG. These physiological findings are in accord with anatomic evidence in humans and in nonhuman primates that the superior temporal cortex contains multiple interconnected auditory areas.     

Efferent cortical connections of multimodal cortex of the superior temporal sulcus in the rhesus monkey.

The cortex of the upper bank of the superior temporal sulcus (STS) in the rhesus monkey contains a region that receives overlapping input from post-Rolandic sensory association areas and is considered multimodal in nature. We have used the fluorescence retrograde tracing technique in order to answer the question of whether multimodal areas of the STS project back to post-Rolandic sensory association areas. Additionally, we have attempted to answer the question of whether the projections from the multimodal areas directed to the parasensory association areas originate from common neurons via axon collaterals or from individual neurons. The results show that multimodal area TPO of the STS projects back to specific unimodal parasensory association areas of the parietal lobe (somatosensory), superior temporal gyrus (auditory), and posterior parahippocampal gyrus (visual). In addition, a substantial number of projections from area TPO are directed to distal parasensory association areas, area PG-Opt in the inferior parietal lobule, areas Ts1 and Ts2 in the rostral superior temporal gyrus, and areas TF and TL in the parahippocampal gyrus. These latter regions are themselves considered to be higher-order association areas. It was also noted that the majority of the projections to these higher-order association areas originate from the middle divisions of area TPO (TPO-2 and TPO-3). These neurons are organized in a significantly overlapping manner. Despite this overlap of the projection neurons, only an occasional double labeled neuron was observed in area TPO. Thus, our observations indicate that the multimodal region of the superior temporal sulcus has reciprocal connections with the unimodal parasensory association cortices subserving somatosensory, auditory and visual modalities, as well as with other post-Rolandic higher-order association areas. These connections from area TPO to post-Rolandic association areas may have a modulating influence on the sensory association input leading to multimodal areas in the superior temporal sulcus.     

Thalamic connections with limbic cortex. I. Thalamocortical projections

The thalamocortical projections to limbic cortex in the cat have been studied with retrograde and anterograde axonal transport techniques. Five limbic cortical areas were identified on the basis of cytoarchitecture. The five areas are the anterior limbic area, the cingular area, the dorsal and ventral retrosplenial areas, and the presubiculum. Each of these cortical areas received small injections of horseradish peroxidase, and the afferent thalamic nuclei were identified by retrograde labelling of cells. The cortical projection of each of the anterior thalamic nuclei and the lateral dorsal nucleus was determined autoradiographically. Each of the anterior thalamic nuclei and the lateral dorsal nucleus projects to limbic cortex by two pathways. One group of fibers leaves the rostral thalamus by the fornix, pierces the corpus callosum, and joins the cingulate fasciculus to reach limbic cortex. The other group travels through the lateral thalamic peduncle and internal capsule. The anterior ventral nucleus projects primarily to the dorsal retroslenial area, particularly to layer I, the deep portion of layer II, and superficial portion of layer III. Sparse projections also exist to the ventral retrosplenial area, the cingular area, and the presubiculum. Very sparse projections to the anterior limbic area are seen. The anterior dorsal nucleus projects primarily to the ventral retrosplenial area, particularly layers I, the deep portion of layer II, and superficial layer III. Sparse projections exist to the dorsal retrosplenial area and presubiculum, but apparently no projections exist to the cingular or anterior limbic area. The anterior medial nucleus projects primarily to layers I and superficial III of the ventral retrosplenial area. Sparse projections exist to each of the other limbic cortical areas. The lateral dorsal nucleus projects extensively onto limbic cortex. Prominent projections occur to layer I, the external granular layer and lamina dessicans of the presubiculum, layers I and III-IV of the dorsal retrosplenial area, and layers I, III, and IV of the cingular area. Sparse projections occur to the ventral retrosplenial area and the anterior limbic areas. Thalamocortical projections also originate in the midline and intralaminar nuclei including the central medial reuniens, rhomboid, paracentral, central lateral, and central dorsal nuclei. These data indicate that the anterior thalamic nuclei project upon limbic cortex in a complex manner. Further, the projections to limbic cortex from the anterior nuclei overlap with projections from the lateral dorsal nucleus. This overlap of thalamic projections onto limbic cortex suggests a convergence of information from nonprimary sensory systems with information from the classical limbic system.     

Cortical afferents to behaviorally defined regions of the inferior temporal and parahippocampal gyri as demonstrated by WGA-HRP.

The inferior temporal gyrus in the monkey appears to be unique among the many extrastriate visual cortices in its importance for normal performance of delayed match-to-sample, a visual memory task. However, the anatomical pathway providing visual information to this portion of the temporal lobe remains unclear. In this study, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was injected into the anterior inferior temporal gyrus and heavy projections were found to arise in cytoarchitectural area TF of the parahippocampal gyrus, as well as moderate projections in more posterior portions of inferior temporal gyrus and perirhinal and entorhinal cortices. Subsequently, WGA-HRP was injected into area TF, resulting in retrogradely labeled cells primarily located in the portions of area TF adjacent to the injection and also in the occipitotemporal sulcus including the ventral portion of the prestriate visual area V4. Moderate projections were found to originate from the dorsal region of area V4 in the lunate sulcus, portions of the caudal parietal lobe, the posterior bank of caudal superior temporal sulcus, and area OPT located at the tip of the superior temporal sulcus. The middle temporal gyrus, foveal prestriate cortex, and area TEO, a transitional area between temporal and occipital visual areas, were all free from retrogradely labeled cells. These latter areas are included in the well-established anatomical system that is known to carry visual information from striate cortex through prestriate to eventually reach dorsal portions of inferotemporal cortex which is coincident with the temporal lobe visual area TE. It is suggested here that there is an additional ventral pathway into area TE as well, which includes projections through portions of the prestriate cortex, occipitotemporal sulcus, and parahippocampal gyrus, ultimately reaching the anterior inferior temporal gyrus, an area that may be specialized to hold visual information over brief periods of time.     

Place of the thalamus in the network of interconnections between the association and limbic cortices in the monkey

Anatomophysiological criteria underlying the definition of associative cortex as well as limbic cortex include some imprecise data. The original notion of "cortical association spheres" (Flechsig) with no connections with the thalamus has rightly been abandoned, and that of the macroscopic "large limbic lobe" (Broca) fails to stand up to histologic or hodologic findings. However, the concept of cortical areas implicated specifically in multiple sensorial integration, sensory-motor coupling and control of behavior lasts due to necessity. In the monkey, the posterior parietal cortex of area 7 (PG area), the cortex of the upper slope of the superior temporal sulcus (STS) and the prefrontal cortex anterior to the sulcus arcuatus exchange direct corticocortical connections, receive afferents from sensory cortex and are not connected to specific thalamic relays. The term "associative" in its widest sense applies more particularly therefore to these cortical areas organized in networks. On the internal surface of the hemisphere, the cingular gyrus, retrosplenial cortex and parahippocampic gyrus (TF and TH areas) which occupy the major part of the limbic lobe, participate in the formation of this network and exchange direct cortico-cortical connections with the associative cortex defined above. The use of anterograde (labelled aminoacids) and retrograde (peroxidases) markers and of fluorescent dyes, allowing double retrograde labelling, demonstrates that the median pulvinar nucleus is connected with the knots of the associative cortical network. This thalamic nucleus, of a relatively increased size from phylogenetic evolution, is therefore excluded from the classification opposing specific and diffuse projection nuclei. In contrast to the thalamic reticular nucleus, which lacks cortical projections, and to the nuclei of the internal medullary band, which have the striatum as main target, the median pulvinar is a thalamic structure connected directly and specifically with each of the cortical areas, lesions of which result in negligence behavior.     

Common cortical and subcortical targets of the dorsolateral prefrontal and posterior parietal cortices in the rhesus monkey: evidence for a distributed neural network subserving spatially guided behavior

Common efferent projections of the dorsolateral prefrontal cortex and posterior parietal cortex were examined in 3 rhesus monkeys by placing injections of tritiated amino acids and HRP in frontal and parietal cortices, respectively, of the same hemisphere. Terminal labeling originating from both frontal and parietal injection sites was found to be in apposition in 15 ipsilateral cortical areas: the supplementary motor cortex, the dorsal premotor cortex, the ventral premotor cortex, the anterior arcuate cortex (including the frontal eye fields), the orbitofrontal cortex, the anterior and posterior cingulate cortices, the frontoparietal operculum, the insular cortex, the medial parietal cortex, the superior temporal cortex, the parahippocampal gyrus, the presubiculum, the caudomedial lobule, and the medial prestriate cortex. Convergent terminal labeling was observed in the contralateral hemisphere as well, most prominently in the principal sulcal cortex, the superior arcuate cortex, and the superior temporal cortex. In certain common target areas, as for example the cingulate cortices, frontal and parietal efferents terminate in an array of interdigitating columns, an arrangement much like that observed for callosal and associational projections to the principal sulcus (Goldman-Rakic and Schwartz, 1982). In other areas, frontal and parietal terminals exhibit a laminar complementarity: in the depths of the superior temporal sulcus, prefrontal terminals are densely distributed within laminae I, III, and V, whereas parietal terminals occupy mainly laminae IV and VI directly below the prefrontal bands. Subcortical structures also receive apposing or overlapping projections from both prefrontal and parietal cortices. The dorsolateral prefrontal and posterior parietal cortices project to adjacent, longitudinal domains of the neostriatum, as has been described previously (Selemon and Goldman-Rakic, 1985); these projections are also found in close apposition in the claustrum, the amygdala, the caudomedial lobule, and throughout the anterior medial, medial dorsal, lateral dorsal, and medial pulvinar nuclei of the thalamus. In the brain stem, both areas of association cortex project to the intermediate layers of the superior colliculus and to the midline reticular formation of the pons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Posterior parietal cortex in rhesus monkey: I. Parcellation of areas based on distinctive limbic and sensory corticocortical connections

Injections of HRP-WGA in four cytoarchitectonic subdivisions of the posterior parietal cortex in rhesus monkeys allowed us to examine the major limbic and sensory afferent and efferent connections of each area. Area 7a (the caudal part of the posterior parietal lobe) is reciprocally interconnected with multiple visual-related areas: the superior temporal polysensory area (STP) in the upper bank of the superior temporal sulcus (STS), visual motion areas in the upper bank of STS, the dorsal prelunate gyrus, and portions of V2 and the parieto-occipital (PO) area. Area 7a is also heavily interconnected with limbic areas: the ventral posterior cingulate cortex, agranular retrosplenial cortex, caudomedial lobule, the parahippocampal gyrus, and the presubiculum. By contrast, the adjacent subdivision, area 7ip (within the posterior bank of the intraparietal sulcus), has few limbic connections but projects to and receives projections from widespread visual areas different than those that are connected with area 7a: the ventral bank and fundus of the STS including part of the STP cortex and the inferotemporal cortex (IT), areas MT (middle temporal) and possibly MTp (MT peripheral) and FST (fundal superior temporal) and portions of V2, V3v, V3d, V3A, V4, PO, and the inferior temporal (IT) convexity cortex. The connections between posterior parietal areas and visual areas located on the medial surface of the occipital and parieto-occipital cortex, containing peripheral representations of the visual field (V2, V3, PO), represent a major previously unrecognized source of visual inputs to the parietal association cortex. Area 7b (the rostral part of the posterior parietal lobe) was distinctive among parietal areas in its selective association with somatosensory-related areas: S1, S2, 5, the vestibular cortex, the insular cortex, and the supplementary somatosensory area (SSA). Like 7ip, area 7b had few limbic associations. Area 7m (on the medial posterior parietal cortex) has its own topographically distinct connections with the limbic (the posterior ventral bank of the cingulate sulcus, granular retrosplenial cortex, and presubiculum), visual (V2, PO, and the visual motion cortex in the upper bank of the STS), and somatosensory (SSA, and area 5) cortical areas. Each parietal subdivision is extensively interconnected with areas of the contralateral hemisphere, including both the homotopic cortex and widespread heterotopic areas. Indeed, each area is interconnected with as many areas of the contralateral hemisphere as it is within the ipsilateral one, though less intensively. This pattern of distribution allows for a remarkable degree of interhemispheric integration.(ABSTRACT TRUNCATED AT 400 WORDS)     

Topographic organization of cortical and subcortical projections to posterior cingulate cortex in the cat: evidence for somatic, ocular, and complex subregions.

The posterior cingulate area (CGp) of the cat consists of cortex on the exposed cingulate gyrus and in the adjacent ventral bank of the splenial sulcus. We have placed deposits of distinguishable fluorescent tracers at multiple restricted sites in CGp and have analyzed the distribution throughout the forebrain of neurons labeled by retrograde transport. Cortical projections to CGp arise (in approximately descending order of strength) from anterior cingulate cortex; prefrontal cortex and premotor areas including the frontal eye fields; visual areas including especially areas 7 and 20b; parahippocampal areas; insular cortex; somesthetic areas; and auditory areas. Corticocortical pathways are organized topographically with respect to the posterior-anterior axis in CGp. Projections from prefrontal cortex and other areas with complex (as opposed to sensory, motor, or limbic) functions are concentrated posteriorly; projections from visual and oculomotor areas are concentrated at an intermediate level; and projections from areas with somesthetic and somatomotor functions are concentrated anteriorly. Thalamic projections to CGp arise from the anterior nuclei (AD, AV, and AM), from restricted portions of the ventral complex (VAd, VAm, and VMP), from discrete sectors of the lateral complex (LD, LPs, and LPm), from the rostral crescent of intralaminar nuclei (CM, PC, and CL), and from the reuniens nucleus. Projections from AM, VAd, LD, and LPs are spatially ordered in the sense that more ventral thalamic neurons project to more anterior cortical sites. Projections from AV and AD are stronger at more posterior cortical sites but do not show other signs of topographic ordering. Projections from LPm, CM, PC, CL, and RE are diffuse. We conclude (1) that cortical afferents of CGp derive predominantly from neocortical areas including those with well established sensory and motor functions; (2) that limbic projections to CGp originate primarily in structures, including the hippocampus, which are associated with memory, as opposed to structures, including the amygdala, which are associated with emotional and instinctual behavior; and (3) that CGp contains subregions in which complex, ocular, or somatic afferents predominate.     

Prefrontal granular cortex of the rhesus monkey. I. Intrahemispheric cortical afferents.

In 6 adolescent rhesus monkeys, unilateral injections of horseradish peroxidase (HRP) were made into 6 regions on the convexity of the prefrontal granular cortex.The afferents to each zone were considered with respect to whether they were local afferents (from adjacent frontal areas) or distal afferents (from outside frontal lobe). The strongest input onto prefrontal granular cortex comes from the temporal lobe and especially areas in and around the superior temporal gyrus. Area 10 in the frontal pole region receives input primarily from area 22 in the superior temporal gyrus and dorsal portion of the superior temporal sulcus. That portion of area 46 above the principal sulcus receives input primarily from area 22 in the upper bank of the superior temporal sulcus while area 46 below the principal sulcus has input from the insula of the superior temporal sulcus and area 21 in the lower bank of the superior temporal sulcus. The cortex within the concavity of the acurate sulcus differs in that the dorsal half (including areas 46 and 8a) receives input primarily from the dorsal bank and to a lesser degree the insula of the superior temporal sulcus while the ventral portion of this region including areas 45 and 46 receives input primarily from the lower bank of the superior temporal sulcus, inferior temporal gyrus and insula of the superior temporal sulcus. Input was noted from cingulate areas 23 and 24 to all 6 injected regions while retrosplenial cortex was noted to project to all but one of the injected regions, i.e. area 10. In addition, some labeled neurons were seen in area 7 after injections into area 46 and some were also seen in the inferior temporal gyrus and parahippocampal region after injections into the arcuate region. Finally, labeled neurons were noted in area 19 after injections into the ventral portion of the prefrontal granular cortex bounded by the arcuate sulcus.The HRP-positive neurons that comprised the intrahemispheric cortical afferents to prefrontal granular cortex were located primarily in layer iii. They were pyramidal in shape and ranged in size from small to medium. These neurons were found to be distributed in a horizontal band in which the number of labeled neurons waxed and waned, or they were distributed in a patchy or clumped manner. The possibility that both patterns of distribution represent a vertical or columnar organization to these afferent neurons is discussed.     

Cortico-cortical projections of the motorcortical larynx area in the rhesus monkey

The efferent cortico-cortical projections of the motorcortical larynx area were studied in three rhesus monkeys (Macaca mulatta), using biotin dextranamine as anterograde tracer. Identification of the larynx area was made with the help of electrical brain stimulation and indirect laryngoscopy. Heavy projections were found into the surrounding ventral and dorsal premotor cortex (areas 6V and D), primary motor cortex (area 4), the homolog of Broca's area (mainly area 44), fronto- and parieto-opercular cortex (including secondary somatosensory cortex), agranular, dysgranular and granular insula, rostral-most primary somatosensory cortex (area 3a), supplementary motor area (area 6M), anterior cingulate gyrus (area 24c) and dorsal postarcuate cortex (area 8A). Medium projections could be traced to the ventrolateral prefrontal and lateral orbital cortex (areas 47L and O), the primary somatosensory areas 3b and 2, the agranular and dysgranular insula, and the posteroinferior parietal cortex (area 7; PFG, PG). Minor projections ended in the lateral and dorsolateral prefrontal cortex (areas 46V and 8B), primary somatosensory area 1 and cortex within the intraparietal sulcus (PEa) and posterior sulcus temporalis superior (TPO). Due to its close spatial relationship to the insula on the one hand and the premotor cortex on the other, the larynx area shows projections which, in some respects, are not typical for classical primary motor cortex.     

Thalamic afferents to the limbic cortex in the cat studied with the method of retrograde axonal transport of horseradish peroxidase

Thalamic afferents to the limbic cortex in the cat were studied with the method of retrograde axonal transport of horseradish peroxidase. The anterior limbic region receives fibers largely from the anteromedial nucleus and partly from the anterodorsal and anteroventral nuclei. There appears to be a dorsoventral organization of cortical projections of the anteromedial nucleus to the anterior limbic region. The cingular area has its main input from the anteroventral and anteromedial nuclei. The lower bank and fundus of the splenial sulcus receive fibers from the anteroventral nucleus, particularly its parvocellular part. The retrosplenial area receives projections from the naterodorsal, anteroventral and anteromedial nuclei. The agranular retrosplenial area (area 30) recieves hardly any fibers from the anterior thalamic nuclei. The postsubicular and presubicular areas receive cortical afferents from the anterodorsal, anteroventral (both magnocellular and parvocellular parts) and anteromedial nuclei. In addition, the limbic cortex receives many fibers from the dorsal lateral, medial pulvinar and lateral pulvinar nuclei, and few fibers from the intralaminar and midline nuclei.