Cruciate Sulcus Research Articles

Multiple integration of input and output in the cortex.

We inserted microelectrodes in eye movement-evoking cortices (EMECs) of cats and examined whether neurones in the EMECs received sensory input from guide signals and fired prior to saccades. The five EMECs were the medial wall of the hemisphere under the cruciate sulcus, the medical and lateral bank of the presylvian sulcus, the fundus of the coronal sulcus and ventral bank of the anterior ectosylvian sulcus. Neurones in all EMECs responded to input guide signals and discharged prior to the saccades. The neurones, however, did not always respond to all saccades, but responded cooperatively or alternatively among the EMECs. These results suggest that input information is projected to a broad area of the cortex and is integrated with output signals in the same cortex to which the input information was projected.

Motor cortical activity during voluntary gait modifications in the cat. II. Cells related to the hindlimbs.

1. To determine whether the motor cortex is involved in the modification of the hindlimb trajectory during voluntary adjustments of the locomotor cycle, we recorded the discharge patterns of 72 identified pyramidal tract neurons (PTNs) within the hindlimb region of pericruciate area 4 during a task in which cats stepped over obstacles attached to a moving treadmill belt. Data were also recorded from representative flexor and extensor muscles of the fore- and hindlimbs contralateral to the recording site. 2. To step over the obstacles, the cats increased flexion sequentially at the knee, ankle, and then the hip to bring the leg above and over the obstacle. This flexion movement was followed by a strong extension of the whole limb that repositioned the foot on the treadmill belt. These changes in limb trajectory were associated with large changes in the level of the activity of many flexor and extensor muscles of the hindlimb, and especially of the knee flexor, semitendinosus. On the basis of the time of onset of the knee and ankle extensor muscles in those steps when the limb was the first to be brought over the obstacle, the swing phase of the modified step cycle was subdivided into two parts, Phase I and Phase II, which correspond respectively to the flexion of the limb (F) and the initial extension (E1). 3. The temporal sequence of the movement was the same whether the hindlimb was the first (lead) or second (trail) to step over the obstacle, although the relative time between flexion at the three joints was changed in the two conditions. 4. Seventy-two PTNs were recorded from the posterior bank of the cruciate sulcus during the voluntary gait modifications. Sixty-three (63/72) of these PTNs had receptive fields that were confined to the contralateral hindlimb, or were recorded from penetrations in which such cells were found. Nine (9/72) PTNs had receptive fields on both the contralateral fore- and hindlimbs. Microstimulation applied through the recording electrode evoked, in all cases, brief twitch responses only in contralateral hindlimb musculature. 5. Forty-two (42/63) of those PTNs with receptive fields confined to the hindlimb showed a significant increase in their discharge frequency when the limb contralateral to the recording site was the first to step over the obstacle (lead limb). Twenty-nine PTNs (29/63) discharged maximally during the swing phase (18 in Phase I and 11 in Phase II), including two PTNS that also increased their discharge frequency during stance.(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of the functional connectivity in the nervous system using time dependent scatter diagrams

We investigated spike trains of the feline nervous system, which are considered to be non-stationary point processes characterized by changes of the functional interneuronal connectivities. Ordinary long-term averaged correlation methods are useful as processing time series data as a quasi-stationary point process, but not as a non-stationary point process. We depicted the joint impulse configuration scatter diagram proposed by D.H. Perkel et al. for subsets of the neural spike train to find changes of functional connectivities The time-dependent scatter diagram wasgenerated by arranging these scatter diagrams in chronological order. Time-dependent scatter diagrams were generated for spike trains derived from the anterior ectosylvius sulcus, the coronal sulcus, the lateral bank of the presylvius sulcus, the medial wall of the presylvius sulcus, the medial wall of the cruciate sulcus. The patterns of time-dependent scatter diagrams for these cortices are considered to change in relation to eye movement. Changes of these patterns correspond to those of the functional connectivities related to the dynamics of eye movement in the neural system.

Topography of commissural fibers in the corpus callosum of the cat: a study using WGA-HRP method

The topography of the commissural fibers in the corpus callosum (CC) of the cat was systematically investigated using the WGA-HRP method. WGA-HRP was injected into various parts of the cerebral cortex and locations of WGA-HRP-stained commissural fibers in the CC were examined. Commissural fibers were arranged in a topological fashion in the CC. Cortical areas rostral to the cruciate sulcus (CrS), corresponding to motor or premotor cortices, projected fibers into the genu of the CC, while fibers from the cortex caudal to the CrS passed through the CC slightly caudal to the genu. When WGA-HRP was injected into the lateral gyrus (LG), it was observed that fibers from the anterior LG passed through the anterior one-third of the CC, whereas those from the posterior LG passed through or near the splenium, and fibers from the middle LG passed between those from the anterior and posterior LG. Similarly, the suprasylvian gyrus (SSG) projected commissural fibers in the CC in a rostrocaudal topological manner. Fibers from the anterior SSG passed through the anterior one-third of the CC, and those from the middle SSG through the middle one-third of the CC and upper part of the splenium. Injection into the most posterior part of the middle SSG revealed fibers passing through the caudal end of the splenium. Callosal fibers from the anterior SSG were focused on in this study, because this area (area 2v) is considered one of the vestibular projection cortices and is an area of special interest to the authors. Callosal fibers from the anterior SSG were observed to pass through the anterior one-third of the body of the CC. When WGA-HRP was injected into auditory areas, fibers from the anterior and middle ectosylvian gyri (ESG) were observed to pass through the posterior one-third of the body of the CC or through the splenium, while fibers from the posterior ESG passed through the splenium. WGA-HRP was also injected into the cingulate gyrus (CiG). Fibers from the anterior CiG (area 24) passed through the anterior portion of the CC while those from the posterior CiG (area 23) passed through the posterior portion of the CC.

Neural projections from the frontal cortex to the oculomotor nucleus: an anatomical study using retrograde axonal, anterograde axonal and transneuronal transport of wheat germ agglutinin-conjugated horseradish peroxidase in cats.

Neural projections from the frontal cerebral cortex to the oculomotor nucleus (3N) were investigated in 1- to 2-year-old cats by retrograde and anterograde axonal and transneuronal transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Following injection of WGA-HRP into the 3N area and its surrounding tissues, retrogradely labeled cells were observed in the anterior sigmoid gyrus, ventral bank of the cruciate sulcus, medial and lateral walls and base of the presylvian sulcus, gyrus rectus and gyrus proreus. Following injection of WGA-HRP into these frontal cortical areas, anterogradely labeled nerve terminals were observed in the mesencephalic periaqueductal gray matter (PAG) just overlying the 3N. Only a few terminals were observed within the 3N. Following injection of WGA-HRP into the extraocular muscles of 1-month-old kittens, transneuronally labeled small cells were observed in the PAG just overlying the 3N and in the mesencephalic reticular formation, ventrolateral to it. These small cells may represent intercalated neurons of the cortico-oculomotor projections in the cat.

Differential impairments in reaching and grasping produced by local inactivation within the forelimb representation of the motor cortex in the cat.

This study analyzed changes in the performance of a reaching task and its adaptive modification produced by reversible inactivation of three sites within the forelimb representation of the motor cortex (MCx, area 4 gamma) in five cats by microinjections of muscimol. Two sites were located in the lateral MCx, rostral (RL-MCx) and caudal (CL-MCx) to the end of the cruciate sulcus, where intracortical microstimulation (ICMS) produced contraction of the most distal muscles. The third site was located more medially, in the anterior sigmoid gyrus (RM-MCx) where ICMS primarily produced contraction of more proximal muscles. The task required the animals to reach into a horizontal target well, located in front of them at one of three possible heights, to grasp and retrieve a small piece of food. The height of the reach was primarily achieved by elbow flexion. Grasping consisted primarily of digit flexion, and food retrieval consisted of forearm supination and shoulder extension. In some blocks of trials, an obstacle was placed in the path of the limb to assess the animal's ability to adaptively adjust the kinematic characteristics of their response trajectory. In normal animals, contact with the bar on the first trial triggered a corrective response at short latency that allowed the paw to circumvent the bar. On all subsequent trials, the trajectory was adapted to prevent contact with the obstacle, with a safety margin of about 1 cm. Inactivation at all sites produced a slowing of movement, a protracted and extended forelimb posture, and increased variability of initial limb position. In addition, inactivation of RL-MCx immediately produced systematic reaching errors, consisting of hypermetric movements, as well as impaired grasping and food retrieval. The degree of hypermetria was similar for all target heights and was not associated with alterations in trajectory control. During inactivation, animals did not compensate for the hypermetria by reducing paw path elevation, suggesting a defect in kinematic planning or in adaptive control. This was confirmed by finding that trajectory adaptation to avoid bar contact was impaired during RL-MCx inactivation. The short latency corrective response, triggered by contact of the limb with the obstacle was, however, preserved. Inactivation of CL-MCx did not impair aiming, grasping, or adaptation immediately after injection. However, impairments occurred after about 1 h postinjection, and at that time mimicked the effects of RL-MCx inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)

SURFACE MORPHOLOGY OF THE FOREBRAIN OF THE BOWHEAD WHALE, BALAENA MYSTICETUS

AbstractObservations were made on 11 brains from bowhead whales subsistence‐harvested by Alaskan Eskimos under International Whaling Commission guidelines. This study is part of a larger project to determine the basic morphology of this endangered species. The bowhead brain is similar to other cetacean brains, particularly that of the southern right whale. Long olfactory peduncles are reflected upon the rostrodorsal surface of the cerebral hemispheres. Olfactory bulbs have not been recovered but are presumed to exist since nerve fibers have been identified histologically in the olfactory peduncles. The induseum griseum is evident on the corpus callosum. The hippocampus proper is small but protrudes into the lateral ventricle. The cruciate sulcus runs diagonally across the rostral surface, limiting a small frontal lobe. The structure of the floor of the sylvian fissure varies from a few short gyri radiating toward the circular sulcus to a more extensive and complex two‐tiered arrangement including numerous gyri perpendicular to the gyrus bordering the paleocortex. Pineal‐body‐like tissue was present in one specimen. There is no interthalamic adhesion. The lateral geniculate body is elevated but smaller than the large medial geniculate body. The neurohypophysis was adherent on most brain specimens received.

Differential connections by intracortical axon collaterals among pyramidal tract cells in the cat motor cortex.

1. Recurrent EPSPs were produced in fast pyramidal tract (PT) cells in the cat motor cortex by stimulation of the medullary pyramid and/or by the glutamate-induced activity of neighbouring PT cells using the spike-triggered averaging (spike-TA) method. 2. In fast PT cells located lateral to the end of the cruciate sulcus, predominantly the motor cortical representation area of the distal forelimb, two components (fast and slow) of recurrent EPSPs were produced by pyramid stimulation. 3. In response to pyramid stimulation, the appearance of the fast and slow components of recurrent EPSPs correlated with the appearance of N1 and N2 field potentials, respectively. 4. The monosynaptic nature of both the fast and slow components of recurrent EPSPs was demonstrated by a double shock test (interstimulus interval less than 5 ms) and high frequency repetitive stimulation (50-100 Hz). 5. The generation of the fast and slow components of recurrent EPSPs was attributed to the synaptic action of recurrent collaterals of fast and slow PT cells, respectively. 6. The amplitude of the slow component of recurrent EPSPs markedly increased with an increase in the stimulus frequency whereas that of the fast component did not, despite the change in stimulus frequency. 7. Selected spike-triggered averaging also revealed frequency facilitation of recurrent individual EPSPs produced in fast PT cells by the activity of single slow PT cells. 8. In fast PT cells located in the anterior and posterior lips of the cruciate sulcus, the motor cortical representation area of the proximal limb or trunk, only the slow component of recurrent EPSPs was produced by pyramid stimulation. 9. It is concluded that the pattern of recurrent connections between neighbouring PT cells differs depending on the motor cortical representation area, and that frequency facilitation of recurrent EPSPs is caused mainly by the input from axon collaterals of slow PT cells.

Connections of the insular cortex in kittens: An anatomical demonstration with wheatgerm agglutinin conjugated to horseradish peroxidase technique

The postnatal development of the afferent and efferent connections of the feline insular cortex was investigated using wheat germ agglutinin conjugated to horseradish peroxidase method. The overall pattern of connections was found to be substantially the same as that observed in adults. In the cortex, anterograde and retrograde labeling was found in the presylvian sulcus, cingulate gyms, cruciate sulcus, medial prefrontal area, lateral suprasylvian cortex, and posterior rhinal sulcus. Subcortical regions containing label included the lateralis medialis-suprageniculate nuclear complex, ventral medial thalamic nucleus, claustrum, lateral amygdaloid nucleus, hypothalamus, and raphe nuclei. In addition, axonal labeling was seen in the striatum, superior colliculus, and pontine nuclei.In contrast, the insular associational projections in kittens differed markedly from those found in adults. In the early postnatal period (1–14 days), dense terminal labeling was found in the cortical layers I, V and VI as well as in the underlying white matter, whereas only moderate to sparse labeling was observed in layers II, III and IV. By four-weeks, an adult-like distribution of terminals was present in each cortical areas: labeling was found mainly in layers I, II, III and IV, with less in layers V and VI.The present results suggest that the basic framework of the insular connections is formed prenatally and that the fine tuning of the axonal terminals and the formation of synapses occurs mainly during the first four postnatal weeks.

Projections from eye movement-evoking cerebral cortices to the striatum and claustrum in the cat

Projection fields in the striatum and claustrum from eye movement-evoking cerebral cortices (EMECs) in the cat were investigated using the WGA-HRP tracing method under electrophysiological guidance to place WGA-HRP in the appropriate sites. The EMECs in the frontal cortex, which are located in the medial wall under the cruciate sulcus (CRUo), the medial and lateral banks of the presylvian sulcus and the knee portion of the coronal sulcus (CORo), projected to the rostral part of the striatum. The EMEC in the temporal cortex, which is located in the ventral bank of the anterior ectosylvian sulcus, projected to the middle part of the striatum. Concerning the EMECs in the frontal cortex, the medially situated CRUo projected to the dorsomedial portion of the striatum, and the laterally situated CORo projected to the ventrolateral portion of the striatum. The dorsal half of the claustrum had reciprocal connections with all of the EMECs.

Raccoon forelimb motorsensory cortex: I. Somatic afferent inputs to different cytoarchitectonic areas

The distribution of potentials evoked in and around forelimb MsI by graded electrical stimulation of forelimb nerves has been studied in the raccoon ( Procyon lotor). These data have been correlated with cytoarchitectonic characteristics of pericruciate cortical tissue. Potentials evoked by cutaneous nerve stimulation were widely distributed in MsI and SmI, but were smaller in amplitude and of longer latency in MsI than in SmI. Stimulation of ulnar, median or deep radial nerve at 1–1.4T, a strength considered to activate only Group I muscle afferent fibers, caused evoked potentials in a localized region mostly confined to posterior sigmoid gyrus. On the basis of cytoarchitectonic features it is concluded that: a) Anterior sigmoid gyrus, to near the level of the tip of the cruciate sulcus, is area 6 cortex; b) The lateral portion of the posterior sigmoid gyrus, cortex comprising the caudal bank of the cruciate sulcus and cortex surrounding the lateral tip of the cruciate sulcus is area 4 cortex; c) The middle portion of the posterior sigmoid gyrus, almost to the lip of the cruciate sulcus rostrally and extending onto the rostral bank of the ascending coronal and postcruciate sulci caudally, is area 3a cortex. The cortical focus for Group I afferent-evoked potentials coincides with area 3a cortex. It is concluded that forelimb MsI of raccoon is organized in a fashion similar to MsI of cats and monkeys.

Corticospinal projections from areas 4 and 6 in the raccoon

The corticospinal projections from areas 4 and 6 were investigated in the raccoon using the horseradish peroxidase (HRP) retrograde tracing technique. Multiple injections of lectin bound HRP and HRP were made into either the cervical or lumbar cord in 7 anesthetized raccoons. Retrogradely labeled neurons were observed throughout a wide extent of areas 4 and 6a beta. The HRP positive cells were most numerous within the dorsal bank of the cruciate sulcus within area 4 and continued around the fundus to occupy the lateral two-thirds of the ventral bank of the cruciate sulcus within area 6a beta. No labeled cells were observed in the more medially located area 6a alpha. Although the HRP positive cells observed following the lumbar cord injections were situated slightly more medial and caudal to those observed following the cervical cord injections, considerable overlap between the two projections was noted. The corticospinal projections arising from areas 4 and 6a beta in the raccoon largely correspond in location to the regions functionally defined as the primary motor cortex and the supplementary motor area, respectively.

Subcortical connections of frontal ‘oculomotor’ areas in the cat

The subcortical connections of the frontal ‘oculomotor’ areas in the medial wall of the hemisphere under the cruciate sulcus (CRUo), the medial (PREo-m) and the lateral banks (PREo-l) of the presylvian sulcus of cats were investigated using WGA-HRP tracing combined with electrophysiologic techniques. Two main modes were identified; one was the common connections to the same targets in the cortico-thalamo-cortical, cerebro-cerebellar and cortico-tectal pathways, and the other was the individual connections to unique portions of the saccade-generating centers in the brainstem. The common reciprocal connections were found in the ventral anterior-ventral lateral complex, principal ventromedial nucleus, rostral intralaminar nuclei, centromedian- parafascicular complex, lateral posterior nucleus, and suprageniculate nucleus. The common efferent projections were in the subthalamic nucleus, lateral habenular nucleus, pretectal nucleus, posterior commisure nucleus, nucleus of Darkschewitsch, pontine nucleus, nucleus reticularis tegmenti pontis, medial accessory inferior olive, and the superior colliculus. The CRUo projected into the ipsilateral field of Forel and paramedial pontine reticular formation (PPRF), the PREo-1 projected into the contralateral dorsomedial medullary reticular formation, and the PRE0-m projected into the ipsilateral medullary reticular formation and there was only a small degree of projection into the central portion between the abducens nerve rootlets.

Thalamocortical connections of the rostral intralaminar nuclei: an autoradiographic analysis in the cat.

In this study the pattern of projections from the rostral intralaminar thalamic nuclei to the cerebral cortex was examined in the cat by autoradiography. Injections of tritiated proline and leucine were placed into the central lateral, paracentral, central medial, and para-stria medullaris nuclei. After injections into the central lateral nucleus, label is present on the lateral side within the presylvian sulcus, in most of the suprasylvian gyrus, including the adjacent lateral and suprasylvian sulci, and in the posterior corner of the ectosylvian gyrus. On the medial side, label is present in the orbitofrontal (Of), precentral agranular (Prag), anterior limbic (La), retrosplenial (Rs), and postsubicular (Ps) areas, as defined by Rose and Woolsey ('48a). The cingulate gyrus also contains label throughout (part of which was defined as the "cingular area," Cg, by Rose and Woolsey, '48a). Label is also found on both banks of the splenial and cruciate sulci. In addition, label is present within the lateral gyrus, on both its lateral and medial sides. The paracentral projections are similar to the central lateral input. On the lateral side, label is found within the presylvian sulcus, suprasylvian gyrus and adjacent lateral and suprasylvian sulci, and posterior ectosylvian gyrus. Medially, label is present in the Of, Prag, La, Cg, Rs, and Ps areas, and within the cruciate and splenial sulci, and in portions of the lateral gyrus. Following injections of the central medial nucleus, label is present in the presylvian sulcus; but in contrast to the central lateral and paracentral projections, the suprasylvian gyrus is labeled only in its posterior part. The central medial nucleus also projects to the posterior lateral gyrus, both laterally and medially. Also, the central medial nucleus projects heavily to rostral cortical zones, which include the Of, Prag and La areas, cruciate sulcus, and the rostral cingulate gyrus. The para-stria medullaris nucleus projects only to the presylvian sulcus and orbitofrontal cortex laterally, but, medially, has an extensive input similar to the central lateral and paracentral projections in that label is present in the Of, Prag, La, Cg, Rs, and Ps areas, in the cruciate and splenial sulci, and in the posterior lateral gyrus. The laminar distribution of label is as follows: the central lateral, paracentral and para-stria medullaris nuclei project primarily to layers I and III, whereas the central medial nucleus projects to layers I and VI. In addition, the central lateral projection has a patchy appearance in the retrosplenial and postsubicular cortices.

Organization of the association cortical afferent connections of area 5: A retrograde tracer study in the cat

The association (intrahemispheric) cortico-cortical afferent connections of area 5 were studied in the cat by means of retrograde tracing techniques involving horseradish peroxidase (HRP) free or wheat germ agglutinin-conjugated (WGA-HRP) or fluorochrome injections. Single or multiple injections were placed in different parts of areas 5a and 5b, the medial division of area 5 (5m), or in the anterior suprasylvian area (SsA). Labeled cells were plotted on projection drawings of the coronal sections and on two-dimensional "maps" of the cerebral cortex, which were produced according to an accurate and consistent procedure. The major findings of this study are: 1. All divisions of the anterior parietal cortex (areas 3a, 3b, 1, and 2) project to area 5 and to SsA. These projections, however, show marked differences in amount and topographical distribution, depending on the mediolateral and rostrocaudal location of the injections. 2. The motor cortex (areas 4 and 6) also projects heavily to area 5 and to SsA in a well-organized topographic fashion: Area 4 projects mainly upon areas 5a, 5m, SsA, and the medial part of 5b; area 6 projects mainly upon the lateral part of 5b and SsA. Moreover, the upper bank of the cruciate sulcus (areas 4 tau and 4 delta) projects to medial parts of area 5, and the lower bank (areas 4 tau, 6a alpha, and 6a beta) projects to lateral parts of area 5. 3. The somatosensory areas in the anterior ectosylvian gyrus and surrounding cortices (SIIm, SII, and SIV) are connected primarily with medial parts of area 5 (particularly 5a), and SsA. 4. Areas 7 and 7m and a number of visual areas (19, SVA, AmLS, PmLS, 21, 20, 18, ALS, and PLS) project in varying degrees to lateral parts of area 5b. Some of these areas also send weak to moderate projections to the medial part of 5b and the lateral part of 5a. 5. Sparse projections arising from the dorsolateral prefrontal, cingular, retrosplenial, granular insular, and suprasylvian fringe cortices were found to distribute in area 5 and SsA, particularly in lateral portions of 5b. 6. Quite abundant intrinsic connections also found, which were loosely organized according to a complex topographic pattern. On the basis of these and previous results (Avendaño et al., 1985), the identity of area 5 in the cat is discussed, and comparisons are made between this area and sectors of adjoining cortex of cat and primates.

Organization and synaptic relationships of the projection from the primary sensory to the primary motor cortex in the cat.

It is known from previous studies that fibers originating from cells in area 2 of the cat primary somatosensory cortex project topographically to area 4 of the motor cortex and that they terminate preferentially in the caudal region of the cruciate sulcus. We examined this pathway to determine more precisely the distribution pattern of fibers and the laminar arrangement of axon terminals in the motor cortex. The recently developed technique of PHA-L staining enabled us to label anterogradely the axons that form this projection. Iontophoretic injections of PHA-L were made into the rostral bank of the ansate sulcus (area 2). After 7 days the cats were perfused and the tissue was processed immunohistochemically to stain the PHA-L filled fibers. Light microscopic examination revealed that a small cluster of cells in the sensory cortex gave rise to multiple foci of labeled axons in area 4. The labeled fibers formed columnlike arrays, which were located for the most part in the posterior bank of the cruciate sulcus and were separated by irregular intervals of cortex devoid of labeled fibers. Clusters of labeled fibers were also found in the anterior region of the cruciate sulcus in some of the animals. The dimensions of the labeled areas and the small number of cells that gave rise to each group of fibers suggested that axonal branches of cells within the injection site formed the multiple foci. Variations in the immunohistochemical staining enabled us to study the laminar distribution of sensory cortex axon terminals with the electron microscope. Whereas some PHA-L labeled terminals were found in the deep cortical layers, the majority (82%) were spread throughout layers I-III. Differences in the laminar distribution of sensory cortex afferents that formed axodendritic or axospinous synapses were noted. Synapses formed with dendritic shafts were relatively sparse (28%) and were confined to the superficial layers. Some of the more numerous axospinous synapses, which accounted for 72% of identified synapses, were found in layers V and VI, although most were in layers I-III. The distribution pattern of terminals showed little variation between columns in different areas of the motor cortex, including that in the anterior cruciate region. The pattern of termination of the sensory to motor cortex projection is discussed in relation to the physiological characteristics of this pathway.

Projections from areas 5 and 7 to subdivisions of the cat sensorimotor cortex

Projections from the parietal cortex (areas 5 and 7) to subdivisions of the sensori-motor cortical region were investigated in cats using axonal degeneration techniques. Differences between the density of distribution of association fibers proceeding from these areas were found within the parietal and sensorimotor cortex. Area 5 projects mainly to the posterolateral portion of the cruciate sulcus (areas 4fu and 4δ) and to fields 4y, 4sfu, 6iffu, 6aa, and 6ab to a lesser extent. Area 7 is connected mainly to the medial portion of the lower lip of the cruciate sulcus (areas 6iffu, 6aa, and 6ab). Somewhat fewer fibers proceed to areas 4fu and 4δ. Fewer projections proceed from the parietal cortex to the somatosensory than to the motor region. Only a few single fibers connect the primary somatosensory region (fields 2, 3a, and 3b) with area 5, while area 7 does not project into this area. Neither field 5 nor 7 projects to the secondary somatosensory cortical area.

Topographical organization of the thalamic afferent connections to the motor cortex in the cat.

The topographical distribution of the cortical afferent connections to the different subdivisions of the motor cortex (MC) was studied in adult cats. The retrograde axonal transport of horseradish peroxidase technique was used. Small single injections of the enzyme were made in the entire MC, including the hidden regions in the depth of the sulcus cruciatus. The areal location and density of the subsequent thalamic neuronal labeling were evaluated in each case. Comparison of the results obtained in the various cases shows that the following: (1) The ventral anterior-ventral lateral complex is the principal thalamic source of afferents to the MC. (2) The ventral medial, dorsal medial, the different components of the posterior thalamic group (lateral, medial, and ventral posteroinferior and suprageniculate nuclei), and the intralaminar, lateral anterior, lateral intermediate, lateral medial, and anteromedial thalamic nuclei are also thalamic sites in which neural projections to the MC arise. (3) The thalamocortical projections to the MC are sequentially organized. The connections arising from the lateral part of the thalamus end in the region of area 4 that is situated medially in the superior lip of the sulcus cruciatus and in the posterior sigmoid gyrus. The projections originating in the most medial thalamic regions terminate in that region of area 6a beta which is located in the medial part of the inferior lip of the cruciate sulcus, and in the anterior sigmoid gyrus. Moreover, the ventral thalamic areas send connections to the most anteriorly located zones of the MC, while the most dorsal thalamic ones project to the most posteriorly located parts of the MC. (4) This shift in the thalamocortical connections is not restrained by cytoarchitectonic boundaries, either in the thalamus or in the cortex. (5) The populations of thalamocortical cells which project to neighboring MC subdivisions exhibit consistent overlapping among themselves. (6) These findings suggest, moreover, that the basal ganglia and the cerebellar projections to the MC through the thalamus are arranged in a number of parallel pathways, which may occasionally overlap.

Organization of cortical and subcortical projections to area 6m of the cat

By analyzing regional variations of afferent connectivity, we have identified a medial subdivision of feline area 6 (area 6m) which differs from all surrounding sectors of the frontal lobe in its pattern of inputs. Area 6m is located in the ventral bank of the cruciate sulcus and on the adjacent medial face of the frontal lobe and is partially coextensive with the medial frontal eye field as identified previously in electrophysiological experiments. Area 6m is innervated by axons from visual, association, and oculomotor areas and does not receive projections from somesthetic or somatomotor areas. Cortical sources of input to area 6m include several retinotopically organized extrastriate visual areas (AMLS, ALLS, and PLLS), association areas with strong links to the visual system (area 7, granular insula, posterior ectosylvian gyrus, and cingulate gyrus), and a lateral division of area 6 (area 61) with oculomotor functions. Thalamic afferents of area 6m derive from the paralamellar ventral anterior nucleus, from a dorsolateral division of the mediodorsal nucleus, and from the rostral intralaminar nuclei. The claustrum and the basolateral nucleus of the amygdala project to area 6m. Projections from area 7, the posterior cingulate area, the ventral anterior nucleus, and the mediodorsal nucleus are spatially ordered in a pattern such that parts of area 6 close to the fundus of the cruciate sulcus receive input from neurons positioned anteriorly in the cortical areas, dorsolaterally in the ventral anterior nucleus, and ventrolaterally in the mediodorsal nucleus. Our results indicate that area 6m probably is involved in the voluntary control of gaze and attention rather than in skeletomotor functions.

Corticocortical connections of frontal oculomotor areas in the cat

The corticocortical connections of the frontal ‘oculomotor’ areas related to eye movements of the cat were studied using the retrograde horseradish peroxidase (HRP) tracing method combined with electrophysiological techniques. The following results were obtained. (1) The medial wall of the hemisphere under the cruciate sulcus (CRU), where contralateral conjugate eye deviation was elicited, received fibers from the medial bank of the presylvian sulcus (PRE). The fundus of the coronal sulcus (COR), where monocular movement of the contralateral eye was evoked, received fibers from the lateral bank of the PRE. (2) All the frontal oculomotor areas, the medial wall of the hemisphere under the CRU, the fundus of the COR, and both banks of the PRE, received fibers from the ipsilateral ventral bank of the anterior ectosylvian sulcus (AES). (3) The ventral bank of the AES recieved fibers from the caudal part of the lateral suprasylvian visual areas. On the basis of the fiber connections, the frontal oculomotor areas can be subdivided into a ‘medial’ area, the medial wall of the hemisphere under the CRU and the medial bank of the PRE, and a ‘lateral’ area, the lateral bank of the PRE and the fundus of the COR. Moreover, we found evidence of fiber projections from the ventral bank of the AES to the frontal oculomotor areas that were physiologically identified.