Biomedical subjects
Publications and source records attributed to M F Sarna.
The companion paper has described a new, fully automatic device for the sorting of action potential waveforms in real time. We present here a brief comparison of performance between this new device and several of the older, more traditional devices used for this purpose. We include in the comparison the performance of 3 human observers.
Under different levels of Nembutal anesthesia the spatiotemporal characteristics of receptive fields of cells in the lateral geniculate nucleus were investigated. All units decreased their maintained activity and bursts of spikes occurred spontaneously after administration of the anesthetic. The excitatory domains of the receptive fields were also changed by shortening of the cell's sustained response and enhancement of the postinhibitory transient responses; the spatial extent of these domains being less affected. A qualitatively new excitatory tertiary domain appeared in the receptive field surround with a latency of 170-300 ms. These effects together with enhancement of the spatiotemporal extent of inhibitory domains suggest that the suppressive action of barbiturate takes place beyond the retina.
A simple amplitude discriminator with two ways of triggering DC-level monitoring is described. This system is based on easily available inexpensive integrated circuits.
The velocity-response curves of the cat's superior colliculus neurons responding to moving stimuli mere studied quantitatively. They were fitted by logarithmic Gaussian curves described by three parameters: optimal stimulus velocity, amplitude and dispersion of the curve. Since reversal of the stimulus movement direction changed neither optimal stimulus velocity nor dispersion of the velocity tuning curve, then the fourth parameter, directional asymmetry, is postulated to describe fully, in conjunction with three parameters mentioned above, the dependence of the neuron response to velocity and direction on the stimulus motion. All parameters were roughly normally distributed and uncorrelated with each other in the sample of cells investigated. Some implications of our results for the classification of cells, and some arguments for population coding against single cell trigger feature coding are discussed.
Spontaneous and evoked activities of nucleus interpositus neurons (IN) of the cerebellum were examined before and after cerebellar paravermal cortex lesions in cats anesthetized with alpha-chloralose. It was found that spontaneous activity increased dramatically following cortical ablation: before the lesion only 4% of cells encountered fired at a rate exceeding 80 impulses/sec., whereas up to 40% discharged at this rate postoperatively. Responses to paw stimulation were also altered: the initial excitation was lengthened from 8.5 to 15.8 msec; narrow; trough causing segmentation in this excitation, which seems to result from Purkinje cell inhibition, was absent; and the succeeding inhibitory period was reduced in duration by 50%. Also after the lesion there was a strong tendency for the neurons to discharge in bursts. It is suggested that changes in cell activity in the IN following cortical lesion unveil neural mechanisms of motor disturbances in lesioned cats.