Moshe Godschalk

Cortical afferents and efferents of monkey postarcuate area: an anatomical and electrophysiological study.

SummaryA study has been made of the corticocortical efferent and afferent connections of the posterior bank of the arcuate sulcus in the macaque monkey. The distribution of efferent projections to the primary motor cortex (MI) was studied by injecting three different fluorescent retrograde tracers into separate regions of MI. The resultant labeling showed a discrete and topographically organized projection: neurons lying below the inferior limb of the arcuate sulcus project into the MI face area, while neurons located in the posterior bank of the inferior limb of the arcuate sulcus and in the arcuate spur region project into the MI hand area. These findings were confirmed electrophysiologically by demonstrating that postarcuate neurons could only be activated antidromically by stimulation within restricted regions of MI. HRP injections within postarcuate cortex indicated that afferents to this region arise from a number of cortical areas. However, the largest numbers of labeled neurons were found in the posterior parietal cortex (area 7b; PF) and in the secondary somatosensory region (SII). Neurons in both 7b (PF) and SII could be antidromically activated by postarcuate stimulation. It was further shown that stimulation of area 7b (PF) gives rise to short-latency synaptic responses in postarcuate neurons, including some neurons with identified projections to MI. The results are discussed in relation to the possible function of the postarcuate region of the premotor cortex in the sensory guidance of movement.

Behaviour of neurons in monkey peri-arcuate and precentral cortex before and during visually guided arm and hand movements

SummaryNeuron activity was recorded in monkey cerebral cortex during a visually guided reaching task. Cells located in the banks of the arcuate sulcus at its curvature changed their activity during the period in which the monkey saw a food reward in a certain position, but before it moved to retrieve the reward. A role of these neurons in visual guidance of arm and hand movements is postulated.

Somatotopy of monkey premotor cortex examined with microstimulation

We reinvestigated the organization of the premotor cortex (PM) using intracortical microstimulation. Movements of forelimb, hindlimb, and orofacial structures were evoked from broad regions of PM that appeared to be contiguous with other motor areas. There were two principal findings: (1) the somatotopy of PM lies roughly parallel to that of the primary motor cortex (MI). Forelimb movements were evoked from sites deep in the caudal bank of the arcuate sulcus and throughout the adjacent cortex bounded by a face representation (laterally) and a hindlimb representation (medially and caudally); (2) unlike the MI, the PM forelimb representation overlaps significantly with its own face representation. PM hindlimb movement sites overlap only slightly with PM forelimb sites, in a manner similar to the MI. There was no obvious boundary between PM, MI, or supplementary motor area hindlimb representations. The present findings are discussed in relation to recently identified subdivisions of the PM.

Slow wave sleep and a state resembling absence epilepsy induced in the rat by γ-hydroxybutyrate

Abstract The effect of γ-hydroxybutyrate (GHB) in relatively low doses (12.5–200 mg/kg) on sleep stages, electrocorticogram (ECoG) patterns and behavior was investigated in the rat. 50–100 mg/kg GHB induced slow wave sleep but, in contrast to the cat, not paradoxical sleep. 200 mg/kg induced a hypersynchronous, bilaterally symmetrical ECoG pattern, which was different in amplitude and frequency distribution from normally occuring high amplitude patterns. When the hypersynchrony occured in bursts, the rats displayed a sudden arrest of motor behavior. Convulsions were not induced. The results, together with the finding of others that GHB is a natural constituent of mammalian brain and our previous observation that the GHB-induced hypersynchrony can be antagonized by anti-absence (anti-petit mal) drugs are discussed in view of the possibility that GHB might play a role in the etiology of absence epilepsy in man.

Eye-movement representation in the frontal lobe of rhesus monkeys

We systematically explored the frontal eye field (FEF), the supplementary eye field (SEF), and nearby regions of the frontal cortex to establish the limits of these or possible adjacent eye-movement fields in macaque monkeys. We found a medio-laterally oriented band of saccadic eye-movement sites that extended from the inferior limb of the arcuate sulcus onto the medial surface of the hemisphere and into the dorsal bank of the cingulate sulcus. Two parts of this region may be outside previously described eye-movement areas. We conclude that eye movements are more broadly represented in the frontal lobes than previously described: either the SEF extends into the dorsal bank of the cingulate sulcus and laterally to the arcuate sulcus, or there are more than two frontal eye-movement fields.

Antagonism of gamma-hydroxybutyrate-induced hypersynchronization in the ECoG of the rat by anti-petit mal drugs

Administration of gamma-hydroxybutyrate (GHB) (200 mg/kg i.p.) in rats evoked a hypersynchronous electrocorticogram pattern which was antagonized by specific anti-petit mal agents, while other antiepileptic drugs exerted no influence, or even potentiated the effect of GHB. The specific sensitivity of the GHB-induced hypersynchrony to anti-petit mal agents suggests a possible use of this effect as a model for testing potential anti-petit mal agents.

Preparation of Visually Cued Arm Movements in Monkey

Single-unit activity was recorded in monkey inferior parietal lobule (IPL) during performance of a visually cued limb motor task. Many neurons in the IPL modulated their activity just after the visual cue was presented, similar to the neuronal activity observed in the premotor cortex in a previous experiment. It is suggested that IPL neurons are involved in preparation of visually cued limb movement. The present results are discussed in view of a possible role for IPL and premotor cortex in processing visual information for use by the primary motor area.

Loss of viable neuronal units in the proximal stump as possible cause for poor function recovery following nerve reconstructions

Function recovery after nerve reconstructions is often poor. Could this be caused by a loss of viable neuronal units proximal to the nerve reconstruction? The number of neuronal units (i.e., a motor or sensory neuron, including its axon and axonal branches) in the proximal segments of reconstructed peripheral nerves were studied using a novel magnetic recording technique. In five rabbits a common personal nerve was transected and microsurgically reconstructed. After 8 weeks regeneration time the nerve compound action signals were recorded magnetically from the reconstructed as well as from the healthy contralateral peroneal nerve and from peroneal nerves of five unoperated control animals. The amplitudes of the recorded signals were compared and the diameter distribution histograms were calculated. These calculations were based on the conduction distance between the stimulator and the sensor and the conduction velocities of 30 different axon diameter classes ranging from 3 to 18 microns. Our results indicate that there is a reduction of approximately 50% in the number of viable neuronal units at 10 mm proximal to a simple nerve reconstruction after 8 weeks regeneration time. The number of neuronal units innervating a hand is strongly correlated with clinical function in a healthy hand. The reduction in viable neuronal units after a reconstruction, demonstrated in our experiments, corresponds with a frequently clinically observed decrease in function after nerve reconstructions. Therefore, we suggest that the number of viable neuronal units may be a good indicator of final functional recovery.

Topography of saccadic eye movements evoked by microstimulation in rabbit cerebellar vermis.

1. We investigated saccadic eye movements elicited by microstimulation in the vermis of the rabbit. Scleral search coils were implanted under the conjunctiva of both eyes and a recording chamber was placed over the cerebellar vermis. 2. Conjugate saccadic eye movements were evoked in lobules VIa, b and c and VII of the vermis by currents ranging from 4 to 60 microA. All movements were horizontal with no apparent vertical component. 3. The cortex on both sides of the vermal mid‐line could be divided in two zones, dependent on the direction of elicited saccades. In the medial zone saccades were directed ipsilaterally, in the lateral zone contralaterally. 4. We conclude that the topography of saccadic eye movements in the rabbit cerebellar vermis is, unlike in monkey and cat, organized in parasagittal zones.

A magnetic evaluation of peripheral nerve regeneration : II. The signal amplitude in the distal segment in relation to functional recovery

Motor and sensory function in a healthy nerve is strongly related to the number of neuronal units connecting to the distal target organs. In the regenerating nerve the amplitudes of magnetically recorded nerve compound action currents (NCACs) seem to relate to the number of functional neuronal units with larger diameters regenerating across the lesion. The goal of this experiment was to compare the signal amplitudes recorded from the distal segment of a reconstructed nerve to functional recovery. To this end, the peroneal nerves of 30 rabbits were unilaterally transected and reconstructed. After 6, 8, 12, 20, and 36 weeks of regeneration time the functional recovery was studied based on the toe‐spread test, and the nerve regeneration based on the magnetically recorded NCACs. The results demonstrate that the signal amplitudes recorded magnetically from the reconstructed nerves increase in the first 12 weeks from 0% to 21% of the amplitudes recorded from the control nerves and from 21% to 25% in the following 23 weeks. The functional recovery increases from absent to good between the 8th and the 20th week after the reconstruction. A statistically significant relation was demonstrated between the signal amplitude and the functional recovery (P < 0.001). It is concluded that the magnetic recording technique can be used to evaluate the quality of a peripheral nerve reconstruction and seems to be able to predict, shortly after the reconstruction, the eventual functional recovery.