Nonequivalent visual, auditory, and somatic corticotectal influences in cat

1. The effects of cortical cooling on the responses of cells to visual, somatic, and acoustic stimuli were studied in the cat superior colliculus (SC). When the visual cortex was cooled, the responses of many visual cells of the SC were depressed or eliminated, but the activity of nonvisual cells remained unchanged. This response depression was found in visual cells located in both superficial and deep laminae and was most pronounced in neurons which were binocular and directionally selective. 2. Cooling somatic and/or auditory cortex had no effect on visual SC cells and, with few exceptions, did not alter the activity of somatic or acoustic cells either. 3. The specificity of visual cortex influences on visual responding in the SC was most apparent in multimodal cells. In trimodal cells, the simultaneous cooling of visual, somatic, and auditory cortex eliminated responses to visual stimuli, but did not affect responses to somatic or acoustic stimuli. Visual responses were returned to the precooling level in both unimodal and multimodal cells by cortical rewarming. 4. The present experiments indicate that despite the organizational parallels among visual, somatic, and acoustic cells of the cat SC, the influences they receive from cortex are non-equivalent. Cortical influences appear to play a more critical role in the responses of visual cells than in the responses of somatic and acoustic cells. These observations raise questions about the functional significance of nonvisual corticotectal systems.     

Topographic organization of monosynaptic reflexes in the cat spinal cord

The topographic organization of monosynaptic reflexes in the cat spinal cord has been studied by comparing the amplitude of reflex discharges recorded from ventral roots consequent to stimulation of dorsal roots entering the cord at different spinal segments. The results indicate that up to 80% of the potentiated monosynaptic reflex discharge recorded from a ventral root can be attributed to afferent input entering the spinal cord at the same segmental level. Moreover, within the same segment, afferents with a more rostral cord entry level exert a stronger synaptic effect on the more rostral portion of the corresponding ventral root.     

Topographic organization of orientation columns in the cat visual cortex

Summary Three-dimensional reconstructions of the orientation column system were obtained from the visual cortex of four cats using the deoxyglucose technique. One cat had normal visual experience, one was monocularly deprived and two had selective experience with vertical and horizontal contours, respectively. In areas 17 and 18 orientation columns form a remarkably regular system of equally spaced parallel bands whose trajectory is orthogonal to the borderline between areas 17 and 18. This topographic organization is resistant to manipulations of early visual experience.     

On the origin of the corticotectal projections in the cat

Summary Stereotaxic injection of horseradish peroxidase into the superior colliculus produced retrograde labelling of layer V pyramides in the Clare Bishop area and the lateral bank of the suprasylvian sulcus, in area 17,18 and 19. Single labelled cells were also found scattered in the splenial, the suprasplenial, the lateral and the suprasylvian gyri. In the cruciate sulcus no labelled cells were observed. Autoradiographically, the lateral bank of the suprasylvian sulcus was also shown to give rise to fibres to the superior colliculus.     

Monocular eye movement in the cat: its corticotectal pathway

The corticotectal pathway from the fundus of the cat's coronal sulcus (CORo) from which monocular movements of contralateral eye were evoked was studied using electrophysiological and anatomical techniques. Neurons in the CORo were activated antidromically by electrical stimulation of the deep layer of the superior colliculus (SC). Labeled cells were found in the CORo following horseradish peroxidase injection in the SC.     

大鼠隔-下托投射定位关系的确定

目的：研究隔—下托投射定位关系。材料与方法：1％WGA—HRP与l0％HRP混合液用微量注射器注射人大民背侧下托，存活36h，取材。海马切片用H2O2—DAB明显色确定注射点位置，隔区切片用TMB显色显示逆行标记神经元。结果：HRP逆行标记细胞主要出现于同侧内侧隔核(MS)和斜带核(NDBV)，Bregma点0．70mm-0．48mm的平面上达到高峰。对侧MS和NDBV仅见少量逆行标记神经元。结论：下托接受同侧MS-NDBV大量神经元投射，其中背海马下托前部与MS—NDBV的中部存在明显定位关系。     

Convergence of retinal W-cell and corticotectal input to cells of the cat superior colliculus

1. Conduction velocities of retinotectal W-cell afferents were estimated from differences among latencies of collicular unit responses to supramaximal stimulation of the contralateral optic disk (OD), optic chiasm (OX), and ipsilateral optic tract (OT). W-cell afferents driving collicular neurons had very slowly conducting axons, nearly all below 8 m/s (mean = 5.3 m/s). These match the conduction velocities of W-cell axons terminating in the uppermost superficial gray layer and triggering juxtazonal potentials (JZPs). Such slow conduction velocities are typical of W-cells belonging to the W2 subclass ("phasic W-cells"), but are slower than nearly all W1 cells ("tonic W-cells"). 2. Most W-driven cells were activated at latencies longer than expected for monosynaptic input from these W-cell afferents. However, comparable delays were observed among JZPs, which signal monosynaptic excitation of collicular neurons by W-cell terminals. This suggests that the delayed activation of W-driven cells reflects slowed conduction in the preterminal segments of W-cell afferents rather than polysynaptic transmission of W-cell signals through intermediary neurons in the brain stem or cortex. Thus monosynaptic inputs from retinal W2 cells appear to drive most neurons of the superficial collicular layers. 3. Convergence of retinotectal W-cell and corticotectal pathways was assessed by recording responses of W-driven collicular cells to intracortical stimulation of area 17. The great majority of W-driven collicular cells were activated by cortical stimulation (41/52; 79%), indicating that such convergence is widespread. 4. The population of corticotectal cells influencing W-driven collicular cells may differ from that mediating Hoffmann's Y-indirect pathway. W-driven collicular cells were activated from the striate cortex at longer latencies (mean = 6.3 ms) than cells driven by the Y-indirect pathway (mean = 2.5 ms). In addition, cortically activated W-driven cells were common throughout the superficial gray layer, whereas cells driven by the Y-indirect input were encountered only in the deepest part of the superficial gray and below. 5. W2 cells, apparently the dominant retinotectal cell type, nearly all project contralaterally and are tuned for slow stimulus velocities. Thus the binocularity of W-driven collicular cells and their sensitivity to moderately fast stimulus motion probably reflect the convergent cortical input described here.     

Topographic representation of vestibular and somatosensory signals in the anuran thalamus

In the isolated brain of the fire-bellied toad, Bombina orientalis, the spatial distribution of vestibular and somatosensory responses in thalamic nuclei was studied following electrical activation of the Vth nerve, the ramus anterior of the VIIIth nerve and of the dorsal roots of spinal nerves 3 and 8. Responses were systematically mapped in frontal planes through the diencephalon at four rostro-caudal levels. The calculated activity maps were superimposed on the outlines of diencephalic nuclei, and those nuclei that received particularly large inputs from the stimulated sensory nerve roots were indicated. Maximal response amplitudes coincided with ventral, central, and posterior thalamic areas and exhibited a topography that differed for each sensory nerve root. Maximal responses evoked from the Vth nerve were largely separated from those from spinal dorsal roots 3 and 8, whereas maximal vestibular responses partly overlapped with those from the other somatosensory nerve roots. Our findings indicate that within the amphibian thalamus sensory signals originating from different nerve roots are largely represented in separate areas as is the case in the thalamus of amniotes. However, the anterior dorsal thalamus which is the only origin of ascending pathways to the medial and dorsal pallium (assumed homologues of the mammalian hippocampus and neocortex, respectively) receives only minor vestibular and somatosensory input. This corroborates the view that amphibians lack a direct sensory thalamo-cortical, or "lemnothalamic," pathway typical of mammals and birds.     

Topographic organization of interaural intensity difference sensitivity in deep layers of cat superior colliculus: implications for auditory spatial representation

Sensitivity to interaural intensity difference (IID) was examined for 103 neurons in the deep layers of superior colliculus (SC) in ketamine barbiturate-anesthetized cats. Noise stimuli were presented dichotically, and IID sensitivity functions were generated while keeping the average binaural intensity (ABI) of stimulation constant. Neurons of three binaural classes were found to be IID sensitive. Neurons receiving excitatory contralateral input and inhibitory ipsilateral input (EO/I cells, 55% of sample) had steplike IID functions, with maximum response at IIDs corresponding to contralateral azimuths (positive IIDs), total suppression at IIDs corresponding to ipsilateral azimuths (negative IIDs), and cutoffs at different positions along the IID axis for different neurons. Neurons responsive only to binaural stimulation (OO/F cells, 15% of sample) had IID functions with a sharp peak in the range of 0 to 10 dB IID. Cells receiving excitatory input contralaterally and a facilitatory ipsilateral input (EO/F cells, 7% of sample) had IID functions of intermediate shape, with a peak in the range of 10 to 20 dB IID and a sharper cutoff near zero IID than at larger positive IIDs. The sharpness of IID cutoff for EO/I cells was quantified by measuring an 80% IID dynamic range. Neurons with 80% IID dynamic ranges of less than 26 dB were judged to have sharp cutoffs. The position along the IID axis of the IID cutoff for these cells was quantified by recording the IID at which the response was at 50% of maximum (half-maximal IID). A topographic organization of EO/I cells with sharp IID cutoffs was found along the rostrocaudal axis of SC, such that rostral EO/I cells had IID functions with half-maximal IIDs near zero, while increasingly caudal EO/I cells had progressively larger (positive) half-maximal IIDs. Although detailed maps could not be obtained in individual animals, the topography was observed in each of nine experiments in which EO/I cells were located in two or more rostrocaudal locations (P = 0.00002). The effect of stimulus level on the stability of IID cutoff was examined for 13 EO/I cells. The majority (85%) showed less than 10 dB variation in half-maximal IID across a range of suprathreshold ABIs, indicating that EO/I cells in SC generally exhibit stability in cutoff with changes in intensity of broadband stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distribution of corticotectal axons from the caudal part of the anterior ectosylvian sulcus in the cat

Axonal projections from cells in cortex surrounding the caudal part of the anterior ectosylvian sulcus (AES) to the superior colliculus (SC) were examined using anterograde tracers. The projection terminates in the medial two-thirds of the deep layers of SC bilaterally, and appears to be topographically organized, perhaps according to the sensory modality (auditory and visual) represented in the caudal part of AES.     

Corticocortical connections of cat primary somatosensory cortex

Summary The organization of corticocortical connections in the representation of the forepaw in cat primary somatosensory cortex (SI) was studied following injections of various tracers into different cortical cytoarchitectonic areas. Small injections of horseradish peroxidase, wheat germ agglutinin-conjugated HRP, Phaseolus vulgaris leukoagglutinin, or fast blue were placed into the representation of the forepaw in areas 3b, 1, or 2. The positions of labeled neurons in SI and the surrounding cortical areas were plotted on flattened surface reconstructions to determine the organization of the corticocortical connections within SI. A strong, reciprocal projection linked the two forepaw representations which have been described in area 3b and the part of area 2 which lies in the anterior bank of the lateral ansate sulcus (see Iwamura and Tanaka 1978a, b). Dense projections also linked these areas with SII, as previously reported (Burton and Kopf 1984a). Additional projections to area 3b arose primarily from areas 3a and 1. Projections to area 2 were more widespread than those to area 3b, and arose from all other areas of SI as well as from areas 4 and 5a. All injections into SI tended to label groups of neurons which lay in mediolateral strips. Corticocortical projection neurons which were most heavily labeled by SI injections were pyramidal cells in layer III. Additional projections from area 2 to 3b, area 5a to 2, and SII to areas 2 and 3b arose from layer VI as well. Although neurons of layers III and VI were always the most densely labeled, large injections into SI labeled neurons in layers II and V as well.     

Types of synapses contacting the soma of corticotectal cells in the visual cortex of the cat

Retrograde transport of horseradish peroxidase has been used to single out a distinct functional cortical cell type for ultrastructural study. Following injection of horseradish peroxidase into the superior colliculus, labelled pyramidal cells were found in layer V of the visual cortex. Examination of the labelled corticotectal cells from the visual cortex showed that their cell bodies received two types of synaptic contacts, one from boutons containing spherical vesicles and one from boutons containing flattened vesicles. The possible functional significance of this dual type of input is pointed out.     

Topographic variations in W-cell input to cat superior colliculus

Summary Most of the retinal input to the cat's superior colliculus (SC) arises from W-cells of the contralateral eye and terminates just below the tectal surface. The goal of this study was to determine whether the strength of this input is uniform over the collicular map or, instead, exhibits topographic variations as has been reported for the retinotectal Y-cell projection (McIlwain and Lufkin 1976). Monosynaptic inputs from the principal W-cell projection mediate the late negative potential (LNP), a collicular field potential that can be evoked by shocks to the optic pathway. We assumed that the amplitude of the potential provided a measure of the strength of the W-cell input to the upper superficial gray layer. Using a fixed stimulus, we measured the maximal amplitude of the LNP at 90 topographically identified tectal sites in 5 cats. The amplitude of the LNP varied as much as 5-fold over the SC and was systematically related to the azimuthal position of the recording site. LNP amplitudes were consistently smallest in the representation of the area centralis and vertical meridian and largest in the representations of the contralateral hemifield periphery and the ipsilateral hemifield. There was little systematic variation in LNP amplitude as a function of elevation in the map. The observed variations did not result from non-uniform activation of retinal afferents or drift in properties of the recording electrodes, stimuli, or preparation. The results suggest that the principal W-cell input to the SC is weaker in the representation of the area centralis than elsewhere in the map. These topographic variations are similar to those reported for the retinotectal Y-cell projection (McIlwain and Lufkin 1976) and are consistent with anatomical evidence for thinning of retinal input in the area-centralis representation (Graybiel 1975; Harting and Guillery 1976; Mize 1983). An important implication of these results is that the scaling of the collicular retinotopic map may not be proportional to the spatial density of tectally projecting W-cells.     

Vestibular and somatosensory interaction in the cat vestibular nuclei

Summary The vestibular nuclei of cats were explored extracellularly with micropipettes to locate units with a resting discharge rate which responded to rotation in the horizontal plane. These units were examined for somatosensory input from neck and limbs. Fewer than half responded to somatosensory stimulation. The neck region was the body area most effective in influencing unitary activity. The response pattern most often noted was an increase and decrease in discharge frequency when the body was moved towards and away from the recording electrode respectively. Change in discharge rate was observed to be primarily dependant upon neck velocity and not upon absolute neck position. Half of the somato-sensory units received input from either the forelimbs or the hindlimbs, while the remaining half responded to both.