Anterior Ectosylvian Research Articles

Relevance of the callosal transfer in defining the peripheral reactivity of somesthetic cortical neurones.

Experiments were performed in 13 chloralose-anaesthetized, curarized cat preparations (monitoring of rectal temperature, heart rate, expired pCO2 and EEG), in order to ascertain whether, and to what extent, the reactivity to ipsilateral skin shocks of the neurones of the anterior ectosylvian and anterior suprasylvian gyri (AEG and ASG, respectively) is dependent on the callosal output of the somatosensory areas of the contralateral hemisphere. Indeed, we knew from previous experiments that a high proportion of AEG and ASG neurones having bilateral peripheral receptive fields (PRFs) can be excited by direct stimulation of the contralateral homonymous areas, and that the callosal fibres originating in the latter carry somesthetic impulses related to contralateral PRFs. A preliminary analysis was carried out on the amplitude and latency relationships between the evoked potentials (EP) recorded simultaneously from the two hemispheres and from the corpus callosum (CC) following stimulation of the forepaw of one side. The results obtained showed good correlations between the onset and development of the EPs picked up from the hemisphere ipsilateral to the stimulated skin, on the one hand, and onset and development of the EPs recorded from the contralateral hemisphere and the corpus callosum, on the other. At a further stage of the experiments, the EPs elicited upon ipsilateral and contralateral skin shocks in the AEG-ASG area have been recorded and averaged before, during and after the reversible inactivation of callosal somesthetic transmission. This was achieved by applying polarizing currents (0.2-1 mA) to the rostral portion of the CC, adequacy and reversibility of this method having been tested by observing, respectively, suppression and prompt restoration of transcallosal EPs and of the asynaptic spiking produced by cortical cells when antidromically invaded from contralateral homotopic cortex. It was seen that during CC blockade the EPs elicited in the AEG-ASG areas did not show any change either in amplitude or time-course if brought about by contralateral peripheral stimulation, whereas those evoked by ipsilateral skin shocks exhibited significant reduction, which was related to the strength of CC polarization and to the reduction of transcallosal EPs. In control experiments similar effects were observed after ablation of somatosensory areas of the hemisphere which send off somesthetic callosal impulses, whereas strychninization of these areas caused effects opposite in sign, i.e., enhancement of the ipsilateral but not of the contralateral EPs in the areas of the untreated hemisphere. By testing the effects of CC polarization on single AEG-ASG neurones, it was observed that the responses of units linked only with contralateral PRFs (Group I; 7 units tested) were unaffected by callosal polarization. The discharges of neurones provided with wide and bilateral PRFs (Group II; 27 units tested) were not affected if elicited by contralateral PRF shocks but were deeply impaired (in 11 neurones out the 27) when provoked by ipsilateral PRF stimulation. The effect consisted chiefly of the disappearance of the first high peak of the PSTHs, and when recording intracellularly graded events, it was mirrored by a large decrease of the postsynaptic excitatory potentials elicited in Group II neurones by ipsilateral PRF shocks. A late scattered histographic component was identified in the PSTHs of such cells, which did not appear to be significantly altered during CC blockade. These effects were observed on the ipsilateral responses of 11 out of the 27 Group II neurones so tested whereas the ipsilateral PSTHs of the remaining 16 Group II neurones either did not undergo significant changes during the callosal blockade or escaped evaluation because of high spontaneous shifts of neural responsiveness. The results are discussed mainly with a view to the possible functional role of the specific somesthetic callosal fibres in defining ipsilateral reactivity for the wide-field cells of the AEG-ASG area.

Steady potential correlates of positive reinforcement and sleep onset in the cat; ‘reward contingent positive variation’ (RCPV)

Summary Nine cats were implanted with epidural non-polarizable Ag-AgCl electrodes over the parieto-occipital and frontal cortex. In addition, similar electrodes were implanted in subjacent white matter of the posterior marginal, medial suprasylvian, and anterior ectosylvian gyri for transcortical recording. Two bone marrow reference electrodes were also used: one in the posterior aspect of the bone overlaying the frontal sinus, and another in the occipital crest. In ‘acute’ anesthetized preparations it was found that the transcortical recording was free from contamination caused by eye-motion potentials. The chronically implanted subjects, kept on 23 h food and water deprivation schedule, were trained to press a lever for 0.5–1 ml of milk reward. Potentials caused by lapping or licking were recorded from an electrode implanted at the bottom of the frontal sinus or in the temporal bone. Eye movements were monitored from an electrode placed in the orbital bone immediately behind the eyeball. After 2–3 weeks of training, all subjects displayed bursts of high-voltage slow-wave activity of 5–9.5 c/sec over the primary and secondary visual projections during consumption of milk reward i.e. , characteristic post-reinforcement synchronization (PRS). The PRS activity was always associated with 200–700 μV positive steady potential (SP) shift over the visual cortex in either transcortical or surface bipolar recording with reference to the anterior ectosylvian gyrus or frontal sinus. This SP shift was contingent upon the presence of light in the test chamber, although the subjects were trained and habituated to perform in the dark; the SP shift was also contingent upon the relative quality and taste of food reward. Therefore, it was termed ‘reward contingent positive variation’ (RCPV). Eye movements, which in several instances could be correlated with relatively small (30–60 μV) positive lambda waves over the visual cortex, did not significantly contribute to the RCPV. In satiated subjects during sleep onset or grooming activity a similar phasic positive SP shift occurred over the same cortical area; it was always associated with or shortly followed by a burst of high-voltage slow-wave activity of 6–8 c/sec; the latter SP shift was termed ‘sleep onset positive variation’ (SOPV). The occurrence of the SOPV was facilitated by the presence of ambient light, but, in distinction to the RCPV responses, it was not absolutely contingent on it. Two relatively small amplitude but rather consistent mirror image reversals of RCPV and SOPV responses were observed: one in the subjacent white matter 3 mm beneath the striate and parastriate cortex, and another at the surface in the immediate periphery of the visual projections, i.e. , over the anterior portions of the ectosylvian, suprasylvian and marginal gyri. The phasic occurrence of SOPV immediately prior to the development of delta slow-wave sleep patterns resulted usually in a cumulative and more stable positive SP shift over the striate cortex. During the peak of a cumulative SOPV a potential difference of approximately 600–700 μV was observed, when measured epidurally across the parieto-occipital cortex between the anterior ectosylvian and posterior marginal gyri. This potential became more diffuse and partially dissipated with the development of slow-wave delta sleep patterns. The PRS, RCPV and SOPV phenomena have been interpreted as processes subserving internal inhibition.

On the direct cortical connections of the neucleus centrum medianum thalami.

AbstractThe center median nucleus of the cat was damaged electrolytically by a horizontally introduced electrode through the cerebellum. After a postoperative survival of ten days to a month degenerated fibers were studied by a modified Nauta method. Direct connections of the center median nucleus of diffuse character were found terminating bilaterally in V–VI layers of the neocortex. Another cortical projection from the center median nucleus terminating in layers III–IV was limited to the anterior and middle regions of the lateral and suprasylvian gyri, the anterior ectosylvian and sylvian gyri and the cornal gyrus. Fibers to the contralateral cortex were found to pass through the corpus callosum.Threshold stimulation of the center median nucleus evoked recruiting response (with a short latency) only in the limited area of the cortex whose direct connections terminate in III–IV layers. Diffuse recruiting response was obtained only with the stronger stimulation. Following lesion of the center median nucleus, diffuse recruiting response, evoked by stimulation of other nonspecific nuclei, was not obtained in the area of the cortex whose III–IV layers recieve connections from the center median nucleus. This supports the view that diffuse recruiting response during stimulation of one nonspecific nucleus is evoked by intrathalamic sprading of impulses to other nonspecific nuclei.

Anterior ectosylvian ablation in the cat.

Anterior ectosylvian ablation in the cat.

Excitatory and Inhibitory Bladder Responses to Stimulation of the Cerebral Cortex in the Cat

AbstractA continuous intravesical pressure recording was established in 22 anesthetized cats by operative canalization of the bladder cavity, leaving the urinary outlet intact. The intravesical pressure variations caused by controlled volume changes were studied, and the alterations in bladder activity in response to stimulation of the cerebral cortex were recorded. The following excitatory bladder reactions on cortical stimulation are described: augmentation of the rhythmic contractions, drop wise expulsion of the bladder contents with incomplete emptying of the vesical cavity and, finally, a normal micturition act with forceful detrusor contractions. With regard to inhibitory effects the following responses were obtained: reduction or complete inhibition of the rhythmic bladder activity, arrest of the urination act or suppressed micturition. In agreement with previous investigations excitatory bladder responses were obtained from the first sensory‐motor area and from the anterior cingulate region. In addition, excitatory effects were elicited by stimulation of the anterior ectosylvian and anterior sylvian gyri (the somatic sensory‐motor area II). Previous observations of inhibitory influence on bladder activity from the first sensory‐motor area were confirmed. In addition, inhibitory effects were produced from the somatic sensory‐motor area II, the subcallosal part of the anterior cingulate region and the orbital gyrus. All the various types of bladder reactions described above were obtained from any of these regions.

Frequency arrangement in anterior ectosylvian auditory cortex of dog

The anterior ectosylvian (AES) area was studied with local applications of strychnine and stimulation of the ear with known frequencies. The threshold spikes for various frequencies were determined to locate the connections to the area. It was found that low frequencies produced spikes ventrocaudally and higher frequencies produced spikes dorsocephalically. Each patch responded to a wider band of frequencies than observed in other areas. The same general arrangement, although less distinct, was obtained for both AES and MES (middle ectosylvian) areas in the lightly anesthetized dog, using only the evoked potentials as indicators. Considerable variation was found between animals and this variation was thought to be due to development of the nervous system. It was found that a sulcus generally separated the AES and MES areas. Other branch sulci of the ectosylvian sulcus penetrated the MES area, distorting the frequency pattern for sounds. The threshold data for the anesthetized dog in the AES and MES areas agree in absolute values to the minimum audible pressure levels for human hearing.

A composite sensory projection area in the cerebral cortex of the cat.

Abstract : Projection of the auditory, vestibular and a part of the somatic system has been shown to overlap extensively in a small cortical, area in the cat, comprising the inferior portions of the anterior ectosylvian and suprasylvian gyri and the compositive gyrus. The responses to each mode of stimulation occur with latencies which suggest that their projection is direct from thalamic relay nuclei. The projection to this area of several sense modalities which have in common their relation to posture and spatial orientation suggest the possibility of a primary cortical area of correlation. (Author)