Modulation of somatosensory evoked responses in the primary somatosensory cortex produced by intracortical microstimulation of the motor cortex in the monkey

Summary Previous studies have shown that the amplitude of somatosensory evoked potentials is diminished prior to, and during, voluntary limb movement. The present study investigated the role of the motor cortex in mediating this movement-related modulation in three chronically prepared, awake monkeys by applying low intensity intracortical microstimulation (ICMS) to different sites within the area 4 representation of the arm. Air puff stimuli were applied to the contralateral arm or adjacent trunk at various delays following the ICMS. Somatosensory evoked potentials were recorded from the primary somatosensory cortex, areas 1 and 3b, with an intracortical microelectrode. The principal finding of this study was that very weak ICMS, itself producing at most a slight, localized, muscle twitch, produced a profound decrease in the magnitude of the short latency component of the somatosensory evoked potentials in the awake money. Higher intensities of ICMS (suprathreshold for eliciting electromyographic (EMG) activity in the target muscle, i.e. that muscle activated by area 4 stimulation) were more likely to decrease the evoked response and produced an even greater decrease. The modulation appeared to be, in part, central in origin since (i) it preceded the onset of EMG activity in 23% of experiments, (ii) direct stimulation of the muscle activated by ICMS, which mimicked the feedback associated with the small ICMS-induced twitch, was often ineffective and (iii) the modulation was observed in the absence of EMG activity. Peripheral feedback, however, may also make a contribution. The results also indicate that the efferent signals from the motor cortex can diminish responses in the somatosensory cortex evoked by cutaneous stimuli, in a manner related to the somatotopic order. The effects are organized so that the modulation is directed towards those neurones serving skin areas overlying, or distal to, the motor output.     

Compensatory motor function of the somatosensory cortex for the motor cortex temporarily impaired by cooling in the monkey

Summary The motor cortex was temporarily impaired by local cooling during repeated execution of visually initiated hand movements in monkeys. The effects of cooling were examined by recording premovement cortical field potentials in the forelimb motor and somatosensory cortices and by measuring reaction time and force exerted by the movement. The cortex was cooled by perfusing cold water (about 1° C) through a metal chamber placed on the cortical epidural surface. Cooling of the forelimb motor area lowered temperature of the cortex under the chamber to 20–29° C within 4–5 min. Recording electrodes for cortical field potentials were implanted chronically on the surface and at 2.5–3.0 mm depth of various cortical areas including that being cooled. Spread of cooling to surrounding cortical areas was prevented by placing chambers perfused with warm water (38–39° C) on the areas.Cooling of the forelimb motor area greatly reduced its premovement cortical field potentials, followed by prolonged reaction times of weakened contralateral wrist muscles. Simultaneous recording from the primary somatosensory cortex revealed an enhancement of its premovement field potentials. All changes were completely reversible by rewarming of the motor cortex. Concomitant cooling of the motor and somatosensory cortices entirely paralysed the contralateral wrist muscles. These results suggest that the motor function of the somatosensory cortex becomes predominant and compensates for dysfunction of the motor cortex when it is temporarily impaired.Supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan     

Short-latency peripheral inputs to thalamic neurones projecting to the motor cortex in the monkey

Summary One hundred seventy-five neurones in the n.ventroposterior lateralis (VPL) and n.ventralis lateralis (VL) in the thalamus of anaesthetised monkeys have been tested antidromically for projection to the cortex and for somatosensory input from the contralateral arm.Using bipolar stimulation of the cortical surface, 113 thalamic neurones were successfully identified as antidromically driven from the hand area of the postcentral gyrus (48 neurones) or from the hand area of the precentral gyrus (65 neurones). All but one of these 113 neurones could only be antidromically discharged from the postcentral cortex or from the precentral cortex, and not from both. Most had antidromic latencies between 0.5 and 1.5 ms.Twenty-five/sixty-five precentrally projecting neurones and 45/48 postcentrally projecting neurones were activated by stimulation of the contralateral median or radial nerves. Both groups responded at short latency (4–8 ms) and many were activated by low-threshold shocks (0.8–1.3 T) and had restricted receptive fields on the hand. Precentrally projecting neurones responded most powerfully to joint movement or deep pressure, and some of these neurones were also responsive to cutaneous stimuli.Precentrally projecting neurones with peripheral inputs were all found in the oral subdivision of the VPL (the VPL_o). The properties of these neurones suggest that they may be partly responsible for rapid somatosensory input to the motor cortex.     

Improved differentiation of tactile activations in human secondary somatosensory cortex and thalamus using cardiac-triggered fMRI

Functional magnetic resonance imaging (fMRI) can reveal human brain activations with high precision. The accuracy may, however, be impaired by movement and deformation of brain tissue associated with cardiac pulsations. Here we corrected for such artifacts by time-locking the fMRI data acquisition to the cardiac cycle in ten subjects who received tactile stimuli to their lips, fingers, and toes. The imaged brain areas covered the parietal operculum and the thalamus, including the secondary somatosensory cortex (SII) bilaterally. Variance of the blood-oxygen-level-dependent signal decreased on average by 38–40% in the SII cortex and by 26% in the thalamus during cardiac triggering compared with conventional imaging. Consequently, statistically significant responses were seen both in the SII cortex and in the ventroposterior thalamus in a larger number of subjects. At the cortical level, the activation pattern revealed two distinct representations for both fingers and toes in the SII region, and the more medial representations were detected with enhanced clarity during cardiac-triggered imaging. In the group-level analysis, the thalamic response to finger stimulation was seen with cardiac triggering, only.     

Compensatory motor function of the somatosensory cortex for dysfunction of the motor cortex following cerebellar hemispherectomy in the monkey

Summary Electrical activities of the motor and somatosensory cortices preceding visually-initiated hand movements were recorded with electrodes chronically implanted on the surface and at 2.5–3.0 mm depth in the cortex of monkeys, and changes in field potentials in these cortices after cerebellar hemispherectomy were observed for many weeks. As previously reported, a unilateral cerebellar hemispherectomy including the lateral and interpositus nuclei eliminates the cerebellar-mediated superficial thalamo-cortical (T-C) responses recorded in the forelimb motor cortex contralateral to the hemispherectomy. These T-C responses normally precede the hand movement, and the operation results in the delay of movement initiation. The electrodes in the forelimb area of the contralateral primary somatosensory cortex showed an enhancement of superficial T-C responses of the somatosensory cortex for 30–40 days after the operation. The enhanced potentials preceded the delayed movement as do the cerebellar-mediated superficial T-C responses of the motor cortex in normal situations. Local cooling of the somatosensory cortex following the cerebellar hemispherectomy disturbed the reaction time movement for a few weeks after the operation. This effect was rarely encountered in normal monkeys. The present study suggests the compensatory motor function of the somatosensory cortex for the dysfunction of the motor cortex in early weeks after cerebellar hemispherectomy.Supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan     

Modulation of the cutaneous responsiveness of neurones in the primary somatosensory cortex during conditioned arm movements in the monkey

Summary The present experiments were designed to investigate the neuronal mechanisms, at the level of the primary somatosensory cortex, which underlie the observation that somatosensory cortical potentials evoked by air puff stimuli directed at the forearm are decreased, in a nonspecific and widespread manner, during voluntary movements about the elbow. Unitary discharge was recorded from 131 cells receiving cutaneous input from the hairy skin of the forearm or hand (areas 3b and 1) of two monkeys trained to perform rapid movements of the contralateral arm (elbow flexion or extension). Evoked unitary responses to air puff stimuli applied to the centre of the cell's receptive field, at various delays before and after the onset of movement, were recorded. Movement produced a significant decrease in the short latency excitatory response to the air puff in 89% of the cells (117/131); the remaining 11% were not modulated by movement. This movement-related gating of cutaneous inputs occurred regardless of the response pattern of the cells to movement alone, being observed in 91% of the cells with no movement-related discharge, and 89% of those with movement-related discharge. The air puff responses of cells with inputs from the forearm and the dorsum of the hand were all similarly modulated by movement and the modulation was clearly present prior to the onset of movement (mean onset, -66 ms). Variation in the depth of modulation as a function of the direction of the movement, flexion or extension, was observed in only a very small proportion of the modulated units (16/117); most showed no relationship to direction. It is suggested that, in this experimental situation, much of the modulation appears to occur at a pre-cortical level since there was no relationship between the pattern of discharge of cells in relation to movement alone and the pattern of movement-related gating of their responses to the air puff. Effects which might be consistent with a cortical origin for the modulation were only infrequently observed. The present results are strikingly similar to those obtained using the evoked potential method, and thus support the hypothesis that, in this task of rapid elbow movements, movement modulates the transmission of cutaneous signals from the hairy skin of the distal forelimb to primary somatosensory cortex in a nonspecific and widespread fashion.     

High-frequency vibratory sensitive neurons in monkey primary somatosensory cortex: entrained and nonentrained responses to vibration during the performance of vibratory-cued hand movements

The activity of high-frequency vibratory sensitive (HFVS) neurons was recorded in monkey primary somatosensory cortex (SI) while animals performed wrist flexions and extensions in response to 57-Hz or 127-Hz palmar vibration. HFVS neurons were distinguished by their exquisite responsiveness to the higher frequency vibration (127 Hz). These neurons probably received input from Pacinian afferents. Systematic selection of HFVS neurons was made using K-means cluster analysis of neuronal firing rates during stimulating at 127 Hz and 57 Hz. HFVS neurons constituted 4% of all recorded cells and more frequently were found in areas 3b, 1, and 2 (5% of total in each area) than in area 3a (1%). Using circular-statistics analyses for nonuniformity of discharges over the vibratory cycle, HFVS neurons were split into two groups of vibration-entrained neurons (E1 and E2 neurons) and one group of nonentrained neurons (NE neurons). E1 neurons were entrained to vibration at both 127 Hz and 57 Hz, whereas E2 neurons were entrained only at one of these vibratory frequencies. Vibration-entrained neurons often exhibited multimodal distributions of interspike intervals (ISIs), with the modes at multiples of the period of vibration. In addition, for these neurons, ISI clusters in joint interval plots commonly had diagonal orientations that were indicative of negative serial correlations of the ISIs, a feature of extrinsically driven rhythmic activity. HFVS neurons located in areas 3a, 3b, and 1 responded to vibration onset at shorter latencies (16.5+1.6, 19.8±5.9, and 21.4±6.4 ms, respectively, during 127-Hz stimulation) than those located in area 2 (35.6±13.8 ms). These observations are consistent with a scheme in which HFVS area 2 neurons receive their inputs from more anterior areas of SI. Moreover, entrained neurons exhibited shorter response latencies than nonentrained neurons. During 127-Hz stimulation, response latencies were 17.3±3.0, 17.5±2.6, and 25.7±6.4 ms for E1, E2, and NE neurons, respectively, located in areas 3a, 3b, and 1. Thus, entrained and nonentrained HFVS neurons may belong to different hierarchical stages of information processing.     

Relationships between sensory responsiveness and premovement activity of quickly adapting neurons in areas 3b and 1 of monkey primary somatosensory cortex

Summary When monkeys make wrist movements in response to vibration of their hands, primary somatosensory (SI) cortical neurons that adapt quickly to the vibratory stimulus often exhibit two temporally separate types of activity. Initially, these neurons respond to the stimulus. They then cease discharging, only to resume firing prior to the movement. This activation, cessation and reactivation occurs even though the sensory stimulus remains on until after the movement is begun. The first change in activity is most likely related to sensory input. The second, which has been called premovement activity, may have a sensory component as well as one related to the upcoming movement. We wanted to test the hypothesis that the premovement activity exhibited when vibration is present represents both a reactivation of a neuron's vibratory response and the premovement activity that normally occurs when vibration is absent. We also wanted to determine if area 3b and 1 quickly adapting (QA) neurons show similar or different activity patterns during the initiation and execution of sensory triggered wrist movements. Four monkeys were trained to make wrist flexion and extension movements in response to vibratory stimuli delivered to the handle which the animals used to control the behavioral paradigm. Two of the four monkeys also made similar wrist movements following visual cues. We found that the premovement activity of QA neurons located in area 1 (but not area 3b) is comprised of a sensory-related component as well as a movement-related component. The magnitude of these individual components differs in relationship to a neuron's receptive field type, the movement direction and the external force imposed on the stimulated forelimb. Premovement activity of area 3b and area 1 QA neurons occurs at the same time prior to movement, regardless of whether visual or vibratory cues are used to trigger wrist movements. This activity occurs at about the same time as others have observed elevations in the threshold for tactile perception, suggesting that premovement activity and changes in sensory responsiveness before movement may be related. These and previous findings are used to construct a model which may predict the firing patterns of SI QA neurons during behavioral tasks. These findings also suggest that areas 3b and 1 may have different roles in processing task-related somatosensory information.     

Interactions between inputs from adjacent digits in somatosensory thalamus and cortex of the raccoon

Interactions between somatosensory afferents arriving from different points in the periphery play an important role in sensory discrimination and also provide the substrate for plasticity following peripheral injury. To examine the extent and time course of such interactions, extracellular recordings were made from neurons in the primary somatosensory cortex and the ventroposterior lateral thalamus of anesthetized raccoons. Interactions between adjacent digits were studied using the conditioning-test paradigm in which a test pulse was delivered to the digit containing the neuron's receptive field (the on-focus digit) at various intervals following conditioning stimulation of an adjacent, off-focus digit. Off-focus stimulation produced predominantly inhibition of the test response with a maximum effect at 20–40 ms in both cortex and thalamus. The mean inhibition was approximately twice as large in the thalamus as in the cortex. Recordings were made in other animals after unmyelinated C fibers had been destroyed in the on-focus digit by subcutaneous injection of capsaicin. This resulted in a doubling of the responses evoked by the test stimulus in both regions, but the spontaneous discharge rate was not changed. The amount of inhibition produced in the cortex was unchanged by capsaicin treatment, but was reduced in the thalamus compared to control animals. This indicates that capsaicin-sensitive peripheral afferents provide a tonic control over interdigit inhibition in the thalamus.     

Movement-related activity of thalamic neurons with input from the globus pallidus and projection to the motor cortex in the monkey

Summary Thalamic neurons projecting to the arm area of the motor cortex were identified by their antidromic response to stimulation of that area in two awake monkeys. Neurons were further identified as receiving inputs from the cerebellar nuclei or the internal segment of the globus pallidus by excitatory or inhibitory response to stimulation of these nuclei. Most (33/34) of the thalamic neurons in the cerebello-thalamo-cortical projection and more than half (12/18) of those in the pallido-thalamocortical projection changed their firing rate on the leverlifting hand movement in the reaction-time task. A considerable number of neurons of both groups (14/23 and 3/10) changed their firing rate prior to the onset of the earliest EMG. These findings agree with the model that activities of pallidal as well as cerebellar nuclear neurons related to motor control are transmitted to the motor cortex through the thalamus.     

Discharge properties of neurones in the hand area of primary somatosensory cortex in monkeys in relation to the performance of an active tactile discrimination task

Summary The discharge patterns of 144 single cortical neurones, within the cutaneous representation of the hand in area 2 (primary somatosensory cortex, SI), were studied in two rhesus monkeys during the performance of an active tactile discrimination task. These were compared to those previously described for units within areas 3b and 1 recorded from the same animals. The task consisted of making a single scanning movement of the digit tips over a surface (first half smooth; second half either smooth or rough). The nature of the texture encountered over the second half of the surface was indicated by the monkey making a differential lever response (push or pull) with the opposite hand. During the task, area 2 units with cutaneous receptive fields (RFs) on the digit tips of interest (those scanned over the surfaces) generally showed an increase in their discharge (75%); patterns of decreased discharge or no modulation (respectively, 12 and 13%) were rarely observed. Units with digital cutaneous RFs not in contact with the stimuli were much more likely to show either a pattern of decreased discharge or no modulation whatsoever (47% in each case), suggesting that there is some selection of cutaneous inputs in this task in that non-active inputs are selectively gated. For units with a cutaneous RF, the sign of modulation changed significantly across SI, in a manner consistent with a pattern of increased convergence onto the more caudal regions of SI. Overall, the proportions of area 2 units with digital RFs on the tips of interest that were classified as either texturerelated (25%) or movement-related (26%) were similar to those reported previously for areas 3b and 1, suggesting that their presumed roles in, respectively, the analysis of surface texture and the representation of the physical parameters of movement are shared and distributed across the three cytoarchitectonic subdivisions of SI under consideration. In addition, the discharge patterns of single texture-related cells in areas 3b, 1 and 2 did not reliably signal whether or not the animal successfully discriminated the surfaces, suggesting that information from a population of cells is required for the performance of the task. Texture-related responses in area 2 were, however, unique in two ways. Firstly, 35% of the texture-related units had additional discharges related to the performance of the scanning movement (texture- and movement-related cells); no such units were found in area 3b, and only one was encountered in area 1. Secondly, the texture-related responses of a subgroup of area 2 units (25%) varied as a function of the order of presentation of the surfaces. As response time also varied with the order of presentation, it is suggested that such cells might represent an intermediate step in the transformation of the sensory input to a behavioural response. Although most units with digital RFs were more responsive during active tactile discrimination than during passive movements of the digits over the same surfaces, secondary factors (speed of movement) were often responsible for this observation. In this aspect, area 2 discharge properties seemed closer to those previously described for area 3b than to those described for area 1. In contrast to both areas 3b and 1, however, the extent of modulation in the task of one-third of the units with larger multi-digit RFs was similar to that produced by classical RF testing, instead of being less (as found for areas 3b and 1). The latter observation suggests that some tactile inputs from the digit tips of interest are transmitted to area 2 relatively unchanged during exploratory movements, and that gating controls in this task of active tactile discrimination may be directed more towards cutaneous inputs to areas 3b and 1 than to area 2.     

Electrophysiological investigations of the somatosensory thalamus of the pigeon

Somatosensory areas in the thalamus of the pigeon were studied electrophysiologically at the single-unit level. Of 459 units, 429 responded to somatosensory stimuli. Of these, 394 units responded specifically to somatosensory stimuli, whereas 8 responded in addition to visual stimuli and 27 to auditory stimuli also (bimodal neurons). Seven units were exclusively driven by visual stimuli and 23 units by auditory stimuli. Recording sites included nucleus dorsalis intermedius ventralis anterior (DIVA) and nucleus dorsolateralis posterior (DLP). The number of bimodal or visual and auditory neurons was much larger in DLP (40%) than in DIVA (7%). This points to a specific somatosensory function of DIVA. There was only a poor somatotopic organization in both nuclei. However, in vertical penetrations, wing representation was usually dorsal to leg representation. Distal parts of the limbs had smaller receptive fields (RFs) than proximal parts, and the smallest RFs were found on the toes, which seem to be represented in most detail.     

Projection on the motor cortex of thalamic neurons with pallidal input in the monkey

Summary The cortical projection areas of thalamic neurons with basal ganglia and/or cerebellar inputs were studied electrophysiologically in unanesthetized monkeys. Thalamic neurons which receive inhibition from the pallidum were found to project to the motor cortex (area 4) as well as to premotor cortex. The neurons with pallidal input and motor cortical projection were located mainly in VLo. This result indicates that the basal ganglia innervate the motor cortex through the thalamus. Thus the basal ganglia can modify the cortical output for controlling movements directly through this pathway as compared with its influence through the prefrontal and premotor cortices.     

Induction of high frequency activity in the somatosensory thalamus of rats in vivo results in long-term potentiation of responses in SI cortex

Summary Extracellular single-unit techniques were employed to record unitary activity simultaneously from the thalamic ventral posterior medial (VPM) nucleus and the ipsilateral primary somatosensory cortex of adult rats. Cross-correlation analysis triggered by the spontaneous firing of thalamocortical relay neurons in VPM and the discharge of layer IV neurons in the corresponding ipsilateral cortical barrel indicated that the paired-units included in this study were strongly correlated in their activity. The baseline responses of highly correlated cortical/thalamic pairs to a 10 ms deflection of a vibrissa on the contralateral side were measured using poststimulus time histograms. After establishing the baseline response, high frequency activity in VPM was induced in one of two ways: i) direct electrical stimulation of thalamic neurons or ii) whisker stimulation in the presence of bicuculline methiodide (BIC) released near the thalamic neurons. Both methods resulted in a conditioning stimulus (CS) paradigm consisting of bursts of high-frequency activity (50–100 Hz) with an inter-burst interval of 150 ms (7 Hz). Almost immediately following the presentation of the CS, the response of layer IV cortical neurons to vibrissa stimulation increased by 37–62% over baseline values, which was maintained after the effects of BIC had worn off in VPM. This enhancement in the response of the cortical neurons was not accompanied by a concomitant increase in the thalamic responses. Thus, these results strongly suggest that the potentiation first occurred at the thalamocortical synapse.     

Reproducibility and stability of neuromagnetic source imaging in primary somatosensory cortex

The present study investigated the test-retest reliability of magnetoencephalography (MEG) source localization of somatosensory evoked fields (SEFs) over an extended time period. Five healthy subjects were stimulated pneumatically at the first and fifth digit in two sessions spaced several months apart. At each location 400 stimuli were presented. The validation of the results was performed by overlay of the dipole localizations into the individual anatomic structure of the subjects' cortex by the use of magnetic resonance images (MRIs). The source localizations of the SEF component were found to be highly reproducible. The mean standard deviation of the dipole locations of the first digit was 1.55 mm in the x-, 1.55 mm in the y- and 3.49 mm in the z-direction. The mean standard deviation of the fifth digit was 3.69 mm in the x-, 4.27 mm in the y- and 6.60 mm in the z-direction. These results support the use of MEG recordings combined with MRI as an adequate method to define the organization of the human primary somatosensory cortex and provide a useful approach to the rapid detection of neuroplasticity.     

Responses of cat motor cortex neurons to cortico-cortical and somatosensory inputs

Summary Intracellular techniques were used to investigate a cortico-cortical path from sensory cortex to motor cortex of cats. Cortico-cortical epsps were evoked in motor cortex neurons by microstimulation of area 3a. Epsps with latencies between 1.2 and 2.4 ms were identified as monosynaptic. These short latency cortico-cortical effects were recorded in layers II through VI of the motor cortex. Neurons with monosynaptic cortico-cortical epsps also received excitatory inputs from forelimb nerves, usually from both muscle and cutaneous afferent fibers. The epsps evoked from forelimb nerves in motor cortex neurons were preceded by neural activity in somatosensory cortex. Time delays between arrival of inputs in sensory cortex and in motor cortex were compared to the latencies of cortico-cortical epsps in the same motor cortex neurons. It was apparent that the timing was appropriate for the identified cortico-cortical path to have relayed some sensory inputs to motor cortex.Supported by the Medical Research Council of Canada (MT-7373, DG-186), the Harry Botterell Foundation for the Neurological Sciences, the Ontario Ministry of Health, and the Faculty of Medicine, Queen's UniversityRecipient of a Medical Research Council of Canada Studentship.Recipient of a Medical Research Council of Canada Fellowship     

Extent of the ipsilateral representation in the ventral posterior medial nucleus of the monkey thalamus

Summary Single and multiunit mapping was used to determine the extent of the representation of ipsilateral structures in the ventral posterior medial (VPM) nucleus of the thalamus in cynomolgus monkeys. The extent of the VPM occupied by terminations of afferent fibers arising in the ipsilateral principal trigeminal nucleus was also determined by anterograde transport of horseradish peroxidase. Both methods indicate that most of the medial half of VPM is occupied by the ipsilateral representation. This is much larger than previously suspected. Units in the medial half of VPM have small, well localized receptive fields on the ipsilateral side of the lower lip, tongue and palate, in the ipsilateral cheek pouch and on the ipsilateral teeth. The representation is largest for the ipsilateral side of the tongue and the cheek pouch. Most units in the lateral half of VPM have small, contralateral receptive fields. Few units in VPM have bilateral receptive fields. VPM is clearly distinguishable by cytochrome oxidase (CO) staining. Anteroposteriorly elongated, CO-positive aggreations correspond to elongated aggregations of units with the same or closely similar receptive fields, especially in the medial, ipsilateral representation.Abbreviations CL Central lateral nucleus - CM Centre médian nucleus - DCN Dorsal cochlear nucleus - DIT Dorsal ipsilateral trigeminal tract - IO Inferior olivary nuclei - ML Medial lemniscus - MV Motor trigeminal nucleus - PRV Principal sensory trigeminal nucleus - SO Superior olivary nuclei - SPV Spinal trigeminal nucleus - Ves Vestibular nuclei - VMb Basal ventral medial nucleus - VPI Ventral posterior inferior nucleus - VPL Ventral posterior lateral nucleus - VPM Ventral posterior medial nucleus - IV Trochlear nucleus - VI Abducens nucleus     

Projections of the precentral motor cortex and other cortical areas of the frontal lobe to the subthalamic nucleus in the monkey

Summary Corticofugal projections were examined by means of the autoradiographic tracer method in 21 macaca fascicularis. The labeled material was injected into the main body representation areas of the precentral motor cortex and into various regions of Brodmann's areas 6, 8 and 9 of the frontal lobe. The ipsilateral subthalamic nucleus receives a moderately strong and somato-topically organized projection from Woolsey's precentral motor cortex. This projection is mainly restricted to the lateral moiety. The remaining nucleus is occupied by less intensive projections from premotor and prefrontal areas. It is concluded that the subthalamic nucleus is a convergence site of pallidal and corticomotor and frontal projections. Cortical afferents may exert an influence on the pallido-subthalamic-pallidal inhibitory feedback loop.     

Projections of the temporo-parietal cortex on vestibular complex in the macaque monkey (Macaca fascicularis)

Summary Connections of the posterior parietal cortex (area 7) with the vestibular complex have been studied in 4 macaque monkeys by anterograde axonal transport methods. WGA-HRP and tritiated amino-acids have been injected in the posterior part of area 7 including the caudal end of the superior bank of superior temporal sulcus and the lateral sulcus. Labeled terminals were observed in the vestibular nuclei complex and distributed bilaterally with a greater ipsilateral contribution. Two main groups of area 7 efferences were found to project to vestibular complex: a) A first group terminates on vestibular nuclei (the inferior vestibular nucleus and the caudal part of the medial nucleus) mainly connected with cerebello-spinal system, b) A second group terminates on vestibular nuclei (the medial and the superior vestibular nuclei and the y group) mainly involved in vestibulo-ocular mechanisms. The prepositus hypoglossi nucleus has also been found to receive area 7 projections. It is concluded that the possible control played by area 7 on the vestibulo-ocular reflex might be exerted through these direct cortico-vestibular projections.     

Tachykinin immunoreactivity in terminals of trigeminal afferent fibers in adult and fetal monkey thalamus

Summary Immunocytochemistry of fetal and adult monkey thalamus reveals a dense concentration of tachykinin immunoreactive fibers and terminals in the dorsolateral part of the VPM nucleus in which the contralateral side of the head, face and mouth is represented. The immunoreactive fibers enter the VPM nucleus from the thalamic fasciculus and electron microscopy reveals that they form large terminals resembling those of lemniscal axons and terminating in VPM on dendrites of relay neurons and on presynaptic dendrites of interneurons. Double labeling strategies involving immunostaining for tachykinins after retrograde labeling of brainstem neurons projecting to the VPM failed to reveal the origin of the fibers. The brainstem trigeminal nuclei, however, are regarded as the most likely sources of the VPM-projecting, tachykinin positive fibers.Abbreviations AB ambiguus nucleus - AN abducens nucleus - C cuneate nucleus - CD dorsal cochlear nucleus - CL central lateral nucleus - CM centre médian nucleus - D dendrite - DR dorsal raphe - DV dorsal vagal nucleus - EC external cuneate nucleus - FM medial longitudinal fasciculus - FN facial nucleus - G gracile nucleus - Gc gigantocellular reticular formation - HN hypoglossal nucleus - ICP inferior cerebellar peduncle - IO inferior olivary complex - LC locus coeruleus - LL lateral lemniscus - LM medial lemniscus - M5 motor trigeminal nucleus - NS solitary nucleus - OS superior olivary complex - P dendritic protrusion - Pb parabrachial nucleus - Pc parvocellular reticular formation - PLa anterior pulvinar nucleus - Pp prepositus hypoglossi nucleus - Ps presynaptic region - Py pyramidal tract - P5 principal sensory trigeminal nucleus - R reticular nucleus - RF reticular formation - RL lateral reticular nucleus - S5 spinal trigeminal nucleus - T terminal - T5 spinal trigeminal tract - VL lateral vestibular nucleus - VM medial vestibular nucleus - VMb basal ventral medial nucleus - VPI ventral posterior inferior nucleus - VPL ventral posterior lateral nucleus - VPM ventral posterior medial nucleus - VR ventral raphe - VS superior vestibular nucleus - VSp spinal vestibular nucleus - ZI zona incerta - 5 trigeminal nerve - 6 abducens nerve - 7 facial nerve