Some electrical measurements of cortical elements and neuronal responses to direct stimulation with particular reference to input resistance

Single-neuron analysis of human thalamus in patients with intention tremor and other clinical signs of cerebellar disease

Tremor that occurs as a result of a cerebellar lesion, cerebellar tremor, is characteristically an intention tremor. Thalamic activity may be related to cerebellar tremor because transmission of some cerebellar efferent signals occurs via the thalamus and cortex to the periphery. We have now studied thalamic neuronal activity in a cerebellar relay nucleus (ventral intermediate-Vim) and a pallidal relay nucleus (ventralis oral posterior-Vop) during thalamotomy in patients with intention tremor and other clinical signs of cerebellar disease (tremor patients). The activity of single neurons and the simultaneous electromyographic (EMG) activity of the contralateral upper extremity in tremor patients performing a pointing task were analyzed by spectral cross-correlation analysis. EMG spectra during intention tremor often showed peaks of activity in the tremor-frequency range (1.9-5.8 Hz). There were significant differences in thalamic neuronal activity between tremor patients and controls. Neurons in Vim and Vop had significantly lower firing rates in tremor patients than in patients undergoing thalamic surgery for pain (pain controls). Other studies have shown that inputs to Vim from the cerebellum are transmitted through excitatory connections. Therefore the present results suggest that tremor in these tremor patients is associated with deafferentation of the thalamus from cerebellar efferent pathways. The thalamic X EMG cross-correlation functions were studied for cells located in Vim and Vop. Neuronal and EMG activity were as likely to be significantly correlated for cells in Vim as for those in Vop. Cells in Vim were more likely to have a phase lag relative to EMG than were cells in Vop. In monkeys, cells in the cerebellar relay nucleus of the thalamus, corresponding to Vim, are reported to lead movement during active oscillations at the wrist. In view of these monkey studies, the present results suggest that cells in Vim are deafferented and have a phase lag relative to tremor that is not found in normal active oscillations. The difference in phase of thalamic spike X EMG activity between Vim and Vop may contribute to tremor because lesions of pallidum or Vop are reported to relieve cerebellar tremor.

Role of peripheral inputs in cerebellar tremor

Tremors reflected in the handwriting in nine right-handed male patients with right-sided cerebellar lesions were studied by reversibly blocking peripheral inputs from the hand. Blocking was achieved by applying a sphygmomanometer cuff over the mid-arm and increasing the pressure up to 200 mm Hg. Evoked potentials from the ulnar nerve and handwriting were monitored in each subject at periodic intervals. Improvement in writing was noticed in 3-5 min in different subjects that coincided with partial reduction of the amplitude of the neurograms. This reduction is consistent with dissociate conduction in a small population of large medullated fibers. On releasing the cuff, the neurograms returned to their normal height within the same time frame of 3-5 min, and the handwriting deteriorated with return of tremor. No change in the handwriting of the volunteers was observed at any stage. The ages of the volunteers ranged from 25 to 48 years and those of the patients from 28 to 56 years. The duration of illness of the patients ranged from 1 to 8 years.

Pathophysiology of cerebellar ataxia

Human and animal experiments performed recently have resulted in a more detailed understanding of limb movement and body posture disorders associated with cerebellar dysfunction. The delay in movement initiation can be explained by a delay in onset of phasic motor cortex neural discharge owing to decreased input from the cerebellar hemispheres. Disorders of movement termination (dysmetria), which can occur for movements at proximal and distal joints, result from disturbances of the timing and intensity of antagonist electromyographic (EMG) activity necessary to break the movement. Disorders in velocity and acceleration of limb movements result from muscular activity that is smaller in amplitude and more prolonged. The cerebellum is important for control of constant force but not for generation of maximal force. Dysdiadochokinesia is explained by a combination of the above mentioned mechanisms. During complex movements in three-dimensional space, the cerebellum contributes to timing between single components of a movement, scales the size of muscular action, and coordinates the sequence of agonists and antagonists. The basic structure of motor programs is not generated in the cerebellum. Hypotonia can be observed only in acute cerebellar lesions. Cerebellar tremor appears to result from a central mechanism, but is modulated or provoked through increased long-loop EMG responses. The common assumption that cerebellar ataxia of stance does not improve with visual feedback is true only of vestibulocerebellar lesions, not for ataxia resulting from atrophy of the anterior lobe of the cerebellum.

Electrophysiological properties of neurons in neonatal rat occipital cortex slices grown in a serum-free medium

The electrophysiological properties of individual neurons within organotypic explants of neonatal rat cortex were examined via intracellular recordings. The explants were grown for two weeks in a serum-free medium. The electrophysiological properties of the neurons within these explants were similar to those reported for both adult cortex in vivo and short-term in vitro slice preparations. The results of the present study show that cortical explants grown under serum-free conditions can serve as a useful model for long-term developmental studies associated with the physiological basis of neural network formation.

The role of the monkey sensory cortex in the recovery from cerebellar injury

The aim of the study was to investigate the contribution of the primary sensory cortex in the compensation of cerebellar deficits during self-paced movements. For this purpose, monkeys were trained on motor tasks which required goal-reaching and independent finger movements. The intermediate and lateral deep cerebellar nuclei and the sensory cortex were lesioned in isolation and in sequence and the course of motor recovery was studied on the test performances. The deep nuclei were lesioned by kainic acid injections, the sensory cortex was removed by ablation. Cerebellar lesions in isolation produced obvious deficits at proximal and distal joints, affecting both slow and fast motor adjustments. Only lesions of the anterior portions of the intermediate and lateral deep nuclear complexes produced deficiencies in voluntary movements. Lesions of the posterior portions produced postural disturbances. The process of recovery following cerebellar lesions was slow and, depending on the nature of the task, was found to be differentially disruptive for motor performances requiring fast and slow motor adjustments. The deficits at distal joints appeared to be more enduring than those at proximal joints. Sensory cortical lesions in isolation produced much less severe and more transient motor deficits. They consisted of hand clumsiness and their recovery was fast and reached higher levels of performance than following cerebellar lesions. When the sensory cortex was removed secondarily to a cerebellar lesion and after recovery from the cerebellar deficits, the initially recovered motor performance became much worse again (decompensation). Removal of the sensory cortex prior to a cerebellar lesion exaggerated the cerebellar deficits and severely limited their recovery. Slow and fast motor performances were completely abolished for three weeks following sequential lesions. Signs of recovery subsequently appeared and stabilized at low levels of performance by five to seven weeks. The effects of combined, sequential cerebellar and sensory cortical lesions were much worse than expected if the effects from the two lesions were merely additive. This indicates that there is some functional interrelationship between the sensory cortex and the cerebellum, which promotes compensation. The somatosensory cortex appears to play a crucial role in the process of recovery from cerebellar motor deficits and it is likely that sensation is an important component in the process of recovery. It is suggested that the sensory cortex exerts its compensatory actions via a structure or structures which receives convergent cerebellar and sensory cortical inputs.

Participation of the cerebellar dentate nucleus in the control of a goal-directed movement in monkeys. Effects of reversible or permanent dentate lesion on the duration and accuracy of a pointing response

Experiments carried out on seven adult baboons were addressed at specifying the participation of the cerebellar dentate nucleus (DN) in the control of duration and accuracy of a goal-directed movement. The visuo-motor task used in this experiment involved trained pointing movement towards stationary target. The monkeys trained to point with the index finger to a target light were required to perform stereotyped movements of constant amplitude and direction, or movements with variable amplitude and direction. Duration of response execution was measured by movement time and accuracy by terminal spatial errors. We analysed the effects of excluding the DN on the arm ipsilateral or contralateral to the partially inactivated nucleus. Two techniques have been used to impair the DN activity: in three monkeys the structure was reversibly cooled with a chronically implanted thermode; in four others partial electrolytic destruction of the DN was performed. In the arm ipsilateral to the lesioned DN we observed modifications of movement times, appearance of systematic errors with increased dispersion. Contralateral effects were restricted to movement times. Changes in movement times and spatial errors were studied over time (4 months) in permanently lesioned animals. Only the spatial dispersion presented a total recovery. These data show that the DN is concerned with the control of speed and accuracy during the execution of visually triggered movements in monkeys. Moreover comparison of results concerning ipsilateral and contralateral effects of DN dysfunction on movement times and errors, and evidence of different time course of recovery in these variables, suggest a differential control exerted by the DN on speed and accuracy of goal directed movements.

Rat cortical neurons in cell culture: culture methods, cell morphology, electrophysiology, and synapse formation

Rat cortical neurons from 15 day embryos are grown in dissociated cell culture and maintained in vitro for 8--12 weeks. The neurons develop into forms which resemble mature cortical neurons in situ, stain with silver and exhibit passive and active electrophysiological properties similar to those of cortical neurons. Extensive chemical excitatory and inhibitory synapses develop de novo. These cultures can provide a model for future studies of mammalian CNS neuronal physiology, transmitter pharmacology, pathophysiology and mechanisms of drug action.

Behavioral development after forelimb deafferentation on day of birth in monkeys with and without blinding

Four infant monkeys underwent somatosensory deafferentation of both forelimbs within hours after birth. Ambulation, climbing, and reaching toward objects developed spontaneously in each case. Thumb-forefinger prehension could be trained by operant shaping methods. Two infants deafferented at birth and blinded by eyelid closure were retarded in motor development by only 1 to 2 weeks. Results indicate that topographic sensory feedback and autogenetic spinal reflexes are not necessary after birth for the development of most types of movement performed by the forelimb musculature in monkeys.

Summated cortical evoked response testing in the deafferented primate

Dorsal rhizotomy from C(2) or C(3) to T(4) in the primate results in failure to elicit summated cortical responses from systematic stimulation of the appropriate peripheral nerves. Under these conditions there is thus no evidence of sensory input into the cerebral cortex. A nonclassical mechanism must therefore be operational to explain the extensive purposive movements observed in the deafferented animals.