Cruciate Sulcus Research Articles

A secondary motor area contributing to interlimb coordination during visually guided locomotion inthecat.

We investigated the contribution of cytoarchitectonic cortical area 4δc, in the caudal bank of the cruciate sulcus of the cat, to the control of visually guided locomotion. To do so, we recorded the activity of 114 neurons in 4δc while cats walked on a treadmill and stepped over an obstacle that advanced toward them. A total of 84/114 (74%) cells were task-related and 68/84 (81%) of these cells showed significant modulation of their discharge frequency when the contralateral limbs were the first to step over the obstacle. These latter cells included a substantial proportion (27/68 40%) that discharged between the passage of the contralateral forelimb and the contralateral hindlimb over the obstacle, suggesting a contribution of this area to interlimb coordination. We further compared the discharge in area 4δc with the activity patterns of cells in the rostral division of the same cytoarchitectonic area (4δr), which has been suggested to be a separate functional region. Despite some differences in the patterns of activity in the 2 subdivisions, we suggest that activity in each is compatible with a contribution to interlimb coordination and that they should be considered as a single functional area that contributes to both forelimb-forelimb and forelimb-hindlimb coordination.

Differential distributions of parvalbumin-positive interneurons in the sulci and gyri of the adult ferret cerebral cortex

Although accumulating evidence suggests that there are significant anatomical and histological differences between the sulci and gyri of the cerebral cortex, whether there is a difference in the distribution of interneurons between the two cortical regions remains largely unknown. In this study, we systematically compared the distributions of parvalbumin-positive interneurons among three neighboring gyrus and sulcus pairs-coronal gyrus and cruciate sulcus, anterior ectosylvian gyrus and rostral suprasylvian sulcus, and posterior ectosylvian gyrus and pseudosylvian sulcus-in the adult ferret cerebral cortex. We proposed a method to partition sulci and gyri into several specific subregions through the deepest points of the sulci and the highest points of gyri in the inner and outer cortical contours of coronal sections. We found that the density of parvalbumin-positive interneurons in the gyri was significantly higher than that in the sulci. Further study revealed that the density of PV interneurons in superficial cortical layers (layers 2/3 and layer 4) was comparable among the three pairs of sulci and gyri. However, the density of parvalbumin-positive interneurons in cortical layers 5/6 was significantly higher in gyri than in sulci. These results indicate that parvalbumin-positive interneurons are differently distributed in infragranular layers of cortical sulci and gyri.

Premotor Cortex Provides a Substrate for the Temporal Transformation of Information During the Planning of Gait Modifications.

We tested the hypothesis that the premotor cortex (PMC) in the cat contributes to the planning and execution of visually guided gait modifications. We analyzed single unit activity from 136 cells localized within layer V of cytoarchitectonic areas 6iffu and that part of 4δ within the ventral bank of the cruciate sulcus while cats walked on a treadmill and stepped over an obstacle that advanced toward them. We found a rich variety of discharge patterns, ranging from limb-independent cells that discharged several steps in front of the obstacle to step-related cells that discharged either during steps over the obstacle or in the steps leading up to that step. We propose that this population of task-related cells within this region of the PMC contributes to the temporal evolution of a planning process that transforms global information of the presence of an obstacle into the precise spatio-temporal limb adjustment required to negotiate that obstacle.

Comparative anatomical description of brain hemisphere surfaces in toninha dolphin and humans

Pontoporia blainvillei (cetacean order and odontoceti suborder), popularly known in Brazil as Toninha, is a small dolphin with a long, thin beak found on the southern shore waters of the western Atlantic. The brain development of dolphins (expressed by the encephalization coefficient) in relation to body size is quite high, and is second only to humans. This high correlation in brain development between dolphins and humans was targeted in this research to describe and compare the morphology of cerebral hemisphere surfaces of these two species. Five brains of Pontoporia blainvillei donated by the BioPesca Project (a non-governmental organization) were analyzed. The brains were fixed in 20% formaldehyde solution for further description and comparison to human brains described in books of neuroanatomy. The telencephalon of Pontoporia blainvillei is rostrally tapered and expanded at the caudal end and it has a greater number of folds/gyrus when compared to human species. Some encephalic grooves/sulcus are similar to grooves found in the human species, such as the cruciate sulcus (central sulcus), lateral fissure (Sylvian cleft), cingulate sulcus and calcarine sulcus. The same encephalic lobes are seen in both species; however the parietal and temporal lobes are highly developed in the Pontoporia blainvillei. These differences are associated with specific function of the species, as the presence of the an efficient auditive system in dolphins.

Distance modulated neuronal activity in the cortical visual areas of cats

During previous studies in cats and monkeys, it was found that in some neurons, responses to visual stimuli of the same angular size were dependent on the absolute distance to these stimuli. To study how widely this peculiarity of visual responses is distributed among cortical visual areas, we recorded activity of neurons in areas V4A, V2, V1, and frontal visual area on the lower bank of the cruciate sulcus. Neuronal activity was recorded at near (20cm) or far (3m) distances from a 3D stationary visual scene. Visual scenes were vertically corrugated light gray screens. Angular dimensions of the screens were the same at short and far distances. Eye movements were free during the test procedure. It was found that about 20% of neurons in areas V4A, V1, and frontal visual area had significantly different levels of activity, while animals were looking at the visual scenes located near or far from the eyes. No neurons with depth modulated activity were found in area V2.

Neural mechanism of activity spread in the cat motor cortex and its relation to the intrinsic connectivity

Motor cortical points are linked by intrinsic horizontal connections having a recurrent network topology. However, it is not known whether neural activity can propagate over the area covered by these intrinsic connections and whether there are spatial anisotropies of synaptic strength, as opposed to synaptic density. Moreover, the mechanisms by which activity spreads have yet to be determined. To address these issues, an 8 × 8 microelectrode array was inserted in the forelimb area of the cat motor cortex (MCx). The centre of the array had a laser etched hole ∼500 μm in diameter. A microiontophoretic pipette, with a tip diameter of 2-3 μm, containing bicuculline methiodide (BIC) was inserted in the hole and driven to a depth of 1200-1400 μm from the cortical surface. BIC was ejected for ∼2min from the tip of the micropipette with positive direct current ranging between 20 and 40 nA in different experiments. This produced spontaneous nearly periodic bursts (0.2-1.0 Hz) of multi-unit activity in a radius of about 400 μm from the tip of the micropipette. The bursts of neural activity spread at a velocity of 0.11-0.24 ms⁻¹ (mean=0.14 mm ms⁻¹, SD=0.05)with decreasing amplitude.The area activated was on average 7.22 mm² (SD=0.91 mm²), or ∼92% of the area covered by the recording array. The mode of propagation was determined to occur by progressive recruitment of cortical territory, driven by a central locus of activity of some 400 μm in radius. Thus, activity did not propagate as a wave. Transection of the connections between the thalamus and MCx did not significantly alter the propagation velocity or the size of the recruited area, demonstrating that the bursts spread along the routes of intrinsic cortical connectivity. These experiments demonstrate that neural activity initiated within a small motor cortical locus (≤ 400 μm in radius) can recruit a relatively large neighbourhood in which a variety of muscles acting at several forelimb joints are represented. These results support the hypothesis that the MCx controls the forelimb musculature in an integrated and anticipatory manner based on a recurrent network topology

PrPSc spreading patterns in the brain of sheep linked to different prion types

Scrapie in sheep and goats has been known for more than 250 years and belongs nowadays to the so-called prion diseases that also include e.g. bovine spongiform encephalopathy in cattle (BSE) and Creutzfeldt-Jakob disease in humans. According to the prion hypothesis, the pathological isoform (PrPSc) of the cellular prion protein (PrPc) comprises the essential, if not exclusive, component of the transmissible agent. Currently, two types of scrapie disease are known - classical and atypical/Nor98 scrapie. In the present study we examine 24 cases of classical and 25 cases of atypical/Nor98 scrapie with the sensitive PET blot method and validate the results with conventional immunohistochemistry. The sequential detection of PrPSc aggregates in the CNS of classical scrapie sheep implies that after neuroinvasion a spread from spinal cord and obex to the cerebellum, diencephalon and frontal cortex via the rostral brainstem takes place. We categorize the spread of PrPSc into four stages: the CNS entry stage, the brainstem stage, the cruciate sulcus stage and finally the basal ganglia stage. Such a sequential development of PrPSc was not detectable upon analysis of the present atypical/Nor98 scrapie cases. PrPSc distribution in one case of atypical/Nor98 scrapie in a presumably early disease phase suggests that the spread of PrPSc aggregates starts in the di- or telencephalon. In addition to the spontaneous generation of PrPSc, an uptake of the infectious agent into the brain, that bypasses the brainstem and starts its accumulation in the thalamus, needs to be taken into consideration for atypical/Nor98 scrapie.

Structural and Immunochemical Characteristics of the Neuronal Organization of Field 4 of the Sensorimotor Cortex in Cats

Inhibitory interneurons in the cortex are regarded as an important intracortical module-forming factor. We report here our studies of the expression of three calcium-binding proteins in interneurons in the sensorimotor cortex of the cat. Calbindin-expressing non-pyramidal neurons were found to be distributed non-uniformly in layer III, forming large groups. Three-dimensional modeling showed that these groups formed continuous columns of width 400-1500 microm, which extended 6000-8000 microm mediolaterally both along the walls of the cruciate sulcus and on the free surfaces of the posterior and anterior sigmoid gyri. These data led to the hypothesis that these groups of inhibitory interneurons may create the conditions for selecting groups of efferent neurons within their areas and to recruit them into a single physiological act.

Phrenic nerve afferent activation of neurons in the cat SI cerebral cortex.

Stimulation of respiratory afferents elicits neural activity in the somatosensory region of the cerebral cortex in humans and animals. Respiratory afferents have been stimulated with mechanical loads applied to breathing and electrical stimulation of respiratory nerves and muscles. It was hypothesized that stimulation of the phrenic nerve myelinated afferents will activate neurons in the 3a and 3b region of the somatosensory cortex. This was investigated in cats with electrical stimulation of the intrathoracic phrenic nerve and C(5) root of the phrenic nerve. The somatosensory cortical response to phrenic afferent stimulation was recorded from the cortical surface, contralateral to the phrenic nerve, ispilateral to the phrenic nerve and with microelectrodes inserted into the cortical site of the surface dipole. Short-latency, primary cortical evoked potentials (1 degrees CEP) were recorded with stimulation of myelinated afferents of the intrathoracic phrenic nerve in the contralateral post-cruciate gyrus of all animals (n = 42). The mean onset and peak latencies were 8.5 +/- 5.7 ms and 21.8 +/- 9.8 ms, respectively. The rostro-caudal surface location of the 1 degrees CEP was found between the rostral edge of the post-cruciate dimple (PCD) and the rostral edge of the ansate sulcus, medio-lateral location was between 2 mm lateral to the sagittal sulcus and the lateral end of the cruciate sulcus. Histological examination revealed that the 1 degrees CEP sites were recorded over areas 3a and 3b of the SI somatosensory cortex. Intracortical activation of 16 neurons with two patterns of neural activity was recorded: (1) short-latency, short-duration activation of neurons and (2) long-latency, long-duration activation of neurons. Short-latency neurons had a mean onset latency of 10.4 +/- 3.1 ms and mean burst duration of 10.1 +/- 3.2 ms. The short-latency units were recorded at an average depth of 1.7 +/- 0.5 mm below the cortical surface. The long-latency neurons had a mean onset latency of 36.0 +/- 4.2 ms and mean burst duration of 32.2 +/- 8.4 ms. The long-latency units were recorded at an average depth of 2.4 +/- 0.2 mm below the cortical surface. The results of the study demonstrated that phrenic nerve afferents have a short-latency central projection to the SI somatosensory cortex. The phrenic afferents activated neurons in lamina III and IV of areas 3a and 3b. The cortical representation of phrenic nerve afferents is medial to the forelimb, lateral to the hindlimb, similar to thoracic loci, hence the phrenic afferent SI site in the cat homunculus is consistent with body position (thoracic region) rather than spinal segment (C(5)-C(7)). The phrenic afferent activation of the somatosensory cortex is bilateral, with the ipsilateral cortical activation occurring subsequent to the contralateral. These results support the hypothesis that phrenic afferents provide somatosensory information to the cerebral cortex which can be used for diaphragmatic proprioception and somatosensation.

Neuronal activities of forebrain structures with respect to bladder contraction in cats

The forebrain is one of the important suprapontine micturition centres. Previous studies have shown that electrical stimulation of the frontal lobe and the anterior cingulate gyrus elicited either inhibition or facilitation of bladder contraction. Patients with frontal lobe tumours and aneurysms showed micturition disorders. Functional brain imaging studies showed that several parts of the forebrain are activated during bladder filling. We aimed to examine neuronal activities of forebrain structures with respect to bladder contraction in cats. In 14 adult male cats under ketamine anaesthesia in which a spontaneous isovolumetric bladder-contraction/relaxation cycle had been generated, we carried out extracellular single-unit recording in forebrain with respect to the contraction/relaxation cycles in the bladder. We recorded 112 neurons that were related to the bladder-contraction/relaxation cycles. Ninety-four neurons were found to be tonically activated during the bladder-relaxation phase, whereas the remaining 18 neurons were tonically activated during the bladder-contraction phase. Both types of neuron were widely distributed around the cruciate sulcus. Most were located medially (medial and superior frontal gyrus) and the rest were located laterally (middle and inferior frontal gyrus). Neurons recorded in forebrain structures were activated with respect to the contraction/relaxation cycles in the bladder. Forebrain structures may have a significant role in regulating bladder contraction in cats.

The cortical representation of sensory inputs arising from bone

In the present study, we show that sensory information from bone reaches the discriminative areas of the somatosensory cortices by electrically stimulating the nerve to the cat humerus and recording evoked potentials on the surface of the primary (SI) and secondary (SII) somatosensory cortex. The SI focus was located over the rostral part of the postcruciate cortex, caudal to the lateral aspect of the cruciate sulcus. The SII focus was identified on the anterior ectosylvian gyrus, lateral to the suprasylvian sulcus. These foci were located adjacent to, or within areas that responded to stimulation of the median, ulnar and/or musculocutaneous nerves. The latency (6–11 ms) to onset of cortical responses in SI and SII were indistinguishable (unpaired t-test; P > 0.05), and were consistent with activation of Aδ fibers in the peripheral nerve. The amplitudes of the cortical responses were graded as a function of stimulus intensity, and may reflect a mechanism for intensity coding. We did not observe long latency cortical responses (50–300 ms) that would be consistent with C fiber activation in the peripheral nerve, and provide evidence that this may be attributable to inhibition of cortical responsiveness following the initial Aδ response. Our finding of discrete, short latency evoked potentials (presumably of Aδ origin) in the primary and secondary somatosensory cortices, following stimulation of a nerve innervating bone, may reflect a mechanism for the discriminative component of bone pain.

Mapping of multisynaptic inputs from the midbrain, diencephalon, and cerebral cortex to phrenic motoneurons using transneuronal transport of rabies virus N2C in the cat

The transneuronal tracer rabies virus N2C can be utilized to the multisynaptic inputs controlling the activity of a muscle, since infected neurons do not quickly exhibit lysis or pathology. In the present study, we injected rabies virus N2C into the diaphragm of cats in order to map the locations of neurons in the midbrain, diencephalon, and cerebral cortex that participate in regulating breathing. Labeled cells in these regions were not evident until after a large number of brainstem neurons were infected, suggesting that the higher centers regulate diaphragm activity indirectly through connections with bulbospinal pathways. The earliest‐infected neurons in the midbrain were located in the nucleus coeruleus, red nucleus, periaqueductal gray, Edinger‐Westphal nucleus, and tegmental fields. When infection became more advanced, additional midbrain areas also exhibited labeling, including the cuneiform nucleus, raphe nuclei, inferior colliculus, and substantia nigra. The earliest‐infected diencephalon neurons were observed in the dorsal and lateral hypothalamic nuclei, although animals with advanced infections also exhibited labeling in a number of hypothalamic areas, the ventral tegmental area, zona incerta, fields of Forel, and a variety of other regions. The first‐infected cortical neurons were located anterior and posterior to the cruciate sulcus (motor cortex), as well as in prefrontal cortical areas. These data suggest that a complex, distributed network of neurons indirectly contributes to controlling diaphragm contractions.

The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats

The aim of the present study was to investigate the relationship between the facial region of the first somatosensory cortex (facial SI) and facial region of the motor cortex (facial MI), as the basis of orofacial behaviors during ingestion of fish paste. Area M in the ventral cortex of the cruciate sulcus that was defined as part of the facial MI by Hiraba et al. (1992 and 1993), showed various facial twitches evoked by intracortical microstimulation (ICMS) and recorded many mastication-related neurons (MRNs). Many MRNs in area M had receptive fields (RFs) in lingual, perioral and mandibular regions. The 60% value of activity patterns of MRNs (n = 124) recorded in area M of normal cats, were the pre-SB type (the sustained and pre-movement type) that showed increased firing prior to the start of mastication and then tonic activity during the masticatory period. MRNs recorded in area M of cats with the facial SI lesion, showed a noticeable decrease in MRNs with RFs in the perioral and mandibular regions and with activity of the pre-SB type. These results strongly suggest that blocking facial SI sensory inputs evoked by mastication interferes with the relay of important facial sensory information to area M required for the appropriate manipulation of food during mastication.

Corticotectal and corticostriatal projections from the frontal eye fields of the cat: an anatomical examination using WGA-HRP

Corticofugal projections from the frontal eye fields (FEF) are believed to access the superior colliculus (SC) directly (i.e., monosynaptically) and indirectly (i.e., multisynaptically) through the basal ganglia. The present results suggest that these two pathways are derived from largely segregated populations of corticofugal neurons. Furthermore, while the different subregions of the FEF from which these pathways originate have different termination patterns in the basal ganglia (i.e., striatum, ST), they share a common termination pattern in the SC. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the two major subdivisions of the FEF (presylvian and cruciate sulci) resulted in dense label in both the ST (bilaterally) and the SC (ipsilaterally). Corticostriatal labeling was found in the caudal part of the head of the caudate nucleus (heaviest ipsilaterally), with labeling from cruciate injections located ventromedial to that produced by presylvian injections. Only presylvian injections resulted in labeling in the putamen. Retrograde tracing experiments demonstrated that both presylvian and cruciate corticostriatal projections originated from neurons in lamina III and the upper aspects of lamina V. An additional but small group of presylvian corticostriatal projections was found in lamina VI. Corticotectal terminal labeling was restricted to the deep laminae of the SC and was derived exclusively from lamina V neurons in cortex. They differed from their corticostriatal counterparts in laminar/sub-laminar location and in soma sizes.

Regional Age-Dependent Effects of Hemineodecortication upon Contralateral Neocortical Thickness: Comparison with Other Measures of Cortical Size

This study investigated age-dependent changes in regional neocortical thickness after hemineodecortication in cats and compared the results to previously reported volumetric and cross-sectional data. Subjects sustained hemineodecortication on postnatal days (P) P10, P30, P60 or in adulthood. Neocortical thickness was quantified at 115 sites along 20 stereotaxic coronal anterior-posterior (AP) planes using defined sites of the main cerebral sulci for the measurements. The analysis established significantly lower thickness values for adult-lesioned as compared to (a) P30, P60 and control groups at AP +14, (b) P30 group at 7 planes along a range of AP +9 to AP +3, and (c) P10 and P60 groups at AP +6. Both the P10 and the P30 groups presented a significantly thicker neocortex than controls at select coronal planes clustering behind AP +10 (parietal and temporal cortices). When analyzed by sulcus, results once again reflected significant advantages for the early-lesioned cats with a significantly thicker cortex found at 4 of the 8 sulci examined. Again, significant advantages were also discovered for early-lesion subjects compared with control cats (splenial, cruciate sulci). Overall, the range of significant effects (from AP +14 to AP 0) and the direction of the means suggested that there was a significant, age-dependent (P10–P60), regional sparing of neocortical thickness with a peak effect occurring at P30. We concluded that: (a) there was a regional sparing/increase of neocortical thickness suggesting that discrete cortical areas are selectively involved in the resistance to structural atrophy following hemineodecortication in young cats (P10–P60) and (b) the global loss of neocortex volume found in our previous study was not apparent using the present thickness measurement. It is suggested that both of these measurements must be taken into account when assessing morphological effects upon the neocortex either in human pathology (i.e. hemispherectomy, intractable epilepsy) or in animal models.

Widespread Distribution of Visual Responsiveness in Frontal, Prefrontal, and Prelimbic Cortical Areas of the Cat: An Electrophysiologic Investigation

By using multiple-unit recording techniques, we explored the visual responsiveness of regions of cortex in and around the area described by others as the cat's “frontal eye fields” (Schlag J, Schlag-Rey M [1970] Brain Res 22:1–13; Guitton D, Mandl G [1978] Brain Res 149:295–312; Pigarev IN [1984] Neirofiziologiia 16:761–766). Our exploration included most of the cat's motor areas (subdivisions of areas 4 and 6) as well as prefrontal and prelimbic regions. Visual responses were routinely obtained from portions of each of the areas we explored, including prefrontal and prelimbic cortex. The qualitative characteristics of visual responses appeared to vary with cytoarchitectonic area. With few exceptions, receptive fields in these areas were large (most exceeding 2,500 deg2) and included the area centralis. Such large fields and inclusion of central vision at nearly all sites precluded retinotopic organization and prevented delineating distinct visual field representations. The most reliable and robust visual activity was observed on the ventral bank of the cruciate sulcus in area 6aα. The regions reported to correspond to the “frontal eye fields” did not exhibit any unique visual properties that distinguished them from surrounding areas. The widespread distribution of visually driven activity we observed is consistent with the known pattern of both cortical and subcortical inputs to this broad region of cortex. The observation of visually responsive activity across broad regions of cortex that is nominally motor is consistent with recent studies involving awake animals. J. Comp. Neurol. 405:99–127, 1999. © 1999 Wiley-Liss, Inc.

Widespread Distribution of Visual Responsiveness in Frontal, Prefrontal, and Prelimbic Cortical Areas of the Cat: An Electrophysiologic Investigation

By using multiple-unit recording techniques, we explored the visual responsiveness of regions of cortex in and around the area described by others as the cat's "frontal eye fields" (Schlag J, Schlag-Rey M [1970] Brain Res 22:1-13; Guitton D, Mandl G [1978] Brain Res 149:295-312; Pigarev IN [1984] Neirofiziologiia 16:761-766). Our exploration included most of the cat's motor areas (subdivisions of areas 4 and 6) as well as prefrontal and prelimbic regions. Visual responses were routinely obtained from portions of each of the areas we explored, including prefrontal and prelimbic cortex. The qualitative characteristics of visual responses appeared to vary with cytoarchitectonic area. With few exceptions, receptive fields in these areas were large (most exceeding 2,500 deg2) and included the area centralis. Such large fields and inclusion of central vision at nearly all sites precluded retinotopic organization and prevented delineating distinct visual field representations. The most reliable and robust visual activity was observed on the ventral bank of the cruciate sulcus in area 6aalpha. The regions reported to correspond to the "frontal eye fields" did not exhibit any unique visual properties that distinguished them from surrounding areas. The widespread distribution of visually driven activity we observed is consistent with the known pattern of both cortical and subcortical inputs to this broad region of cortex. The observation of visually responsive activity across broad regions of cortex that is nominally motor is consistent with recent studies involving awake animals.

Comparison of the cortical connections of areas 4 gamma and 4 delta in the cat cerebral cortex.

Area 4 of the cat cerebral cortex has been subdivided into several regions based on cytoarchitectonic studies: areas 4 gamma, 4 delta, 4sfu, and 4fu (Hassler and Muhs-Clement [1964] J. Hirnforsch. 6:377-420). In a previous study, we found separate representations of contralateral limb movements in areas 4 gamma and 4 delta (Ghosh [1997] J. Comp. Neurol. 380:191-214). To investigate the relationship between these representations, the ipsilateral cortical connections of area 4 gamma and 4 delta were compared by the use of the retrograde neural tracers. After intracortical microstimulation of area 4, tracer was injected into one or two of the following regions: the forelimb regions of the rostral and caudal subdivisions of areas 4 gamma and 4 delta (r4 gamma, r4 delta, c4 gamma, c4 delta, separated by the cruciate sulcus) and the hindlimb regions of c4 gamma and c4 delta. Retrogradely labeled neural profiles were counted in every fourth section of the coronal series and located in cytoarchitectonic areas of the ipsilateral cortex. We found topographically organized reciprocal connections between areas 4 gamma and 4 delta; these connections were part of a rich network of interconnections between the cytoarchitectonic subdivisions of area 4. The forelimb regions of c4 gamma and c4 delta, of r4 gamma and c4 delta, and of r4 gamma and r4 delta were interconnected. These findings support the location of a secondary motor area in 4 delta. No interconnections between the forelimb regions of r4 gamma and c4 gamma, and of r4 delta and c4 gamma, could be found. Area 6 (particularly area 6a gamma) was found to project strongly to the forelimb regions of r4 gamma and r4 delta and relatively weakly to the forelimb region of c4 delta. Retrogradely labeled neurons were also detected in areas 3a, 3b, 1, 2pri, 5, 7, and insula after tracer injections in area 4.

Identification of motor areas of the cat cerebral cortex based on studies of cortical stimulation and corticospinal connections.

The location and topography of motor areas in the cat cerebral cortex were studied by electrical stimulation of the cortex in five animals, and by the injection of retrograde tracers into the spinal cord of four animals. Movements evoked by intracortical microstimulation (ICMS) of the anterior, posterior and lateral sigmoid gyri, both banks of the cruciate sulcus and the dorsal bank of the presylvian sulcus were observed in anaesthetized cats. Fluorescent tracers (Fast Blue and/or Diamadino Yellow) were injected into the lateral funiculus in the second cervical segment, into the gray matter of cervical segments C3-T1 and/or into the gray matter of lumbar segments L2-S1. Contraction of the contralateral forelimb, hindlimb or facial muscles was observed following electrical stimulation of several cytoarchitectonic areas: 4 gamma, 4 delta, 6a alpha, 6a gamma, and 3a. These findings suggested representations of contralateral forelimb and hindlimb movements in areas 4 gamma and 4 delta, and of the contralateral forelimb muscles in areas 6a alpha and 6a gamma. Corticospinal neurons were located in all the above cytoarchitectonic areas as well as in areas 3b, 1, 2, 2pri, and 5. Large numbers of neurons were labeled in areas 4 gamma and 4 delta, and moderate labeling was observed in areas 6a gamma and 6a alpha. Corticospinal neurons projecting to cervical and lumbar segments were located in areas 4 gamma and 4 delta, while those projecting only to cervical segments were detected in areas 6a alpha and 6a gamma. Based on these findings it is proposed that within the motor cortex of the cat there are representations of limb movements in several cytoarchitectonic subdivisions. Many of these representations may be candidate secondary motor areas.

Cerebellar nuclear projection of single axons of inferior olive neurons of the rat

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.