Cat Somatosensory Cortex Research Articles

Pyramidal tract activity associated with a conditioned hand movement in the monkey.

Pyramidal tract activity associated with a conditioned hand movement in the monkey.

Intracellular potentials from “idle” cells in cerebral cortex of cat

Intracellular recording was carried out in “idle” cells from somatosensory, motor and anterior suprasylvian cortex of cat. The cells were studied simultaneously with examination of the DCR, spreading cortical depression, responses to stimulation of midline and postero-ventral thalamic nuclei, and Metrazol-induced seizure discharge. 1. 1. Observations were made on 70 cells showing resting membrane potentials of 50–80 mV. “Idle” cells show no injury discharge upon impalement and no spontaneous firing. During repetitively evoked DCR, and responses to repetitive stimulation (6–60/sec) of midline and postero-ventral thalamic nuclei, “idle” cells show a slow depolarizing response (SDR). The depolarization can attain a magnitude of 20 mV, summates and outlasts the stimulus period for one or more sec. The SDR never gives rise to cell discharge and closely corresponds in configuration to the evoked surface-negative shifts. If stimulation fails to evoke surface slow negativity, it produces no change in the intracellular record. 2. 2. During spreading cortical depression, a marked membrane depolarization (20–40 mV) occurs. Duration and configuration of the depolarization approximates the negative SP shift that accompanies the depression. During this sustained depolarization, a surface stimulus is no longer capable of producing an SDR. Upon recovery of resting membrane potential, surface stimulation once again evokes an SDR. 3. 3. After i.v. injection of Metrazol, there is a reduction in membrane potential followed by appearance of transient membrane depolarizations. Each depolarization corresponds closely to a paroxysmal wave recorded at the surface. 4. 4. The alternatives that “idle” cells are neuroglia, pyramidal cell dendrites or short axon cells are discussed.

On the nature of the primary evoked response

The hypothesis that the primary evoked response results from the summation of slow postsynaptic potential changes on synaptically driven neurons near the recording electrode is tested in this research by a computer simulation. On the assumption that cortical resistivity remains relatively constant through depth in the cerebral cortex and through time during afferent input, net current is proportional to grad V. The vertical component of net current flow in the cat's somatosensory cortex was measured during the primary evoked response and a method was devised for fractionating this current into a major part, due to s neurons (see footnote 2), and a minor part, due to m neurons. A model of the distribution of extracellular current flow was developed and, with the use of histological and neuronal population response data, the vertical component of net current flow due to s neurons was calculated. The experimentally derived and the calculated patterns of vertical current flow were found to be alike in all major features, thus strongly supporting the hypothesis under test. The weak currents due to m neuron response were not simulated in this study.

Slow and fast groups of pyramidal tract cells and their respective membrane properties.

Slow and fast groups of pyramidal tract cells and their respective membrane properties.

Response properties of neurons of cat's somatic sensory cortex to peripheral stimuli.

Response properties of neurons of cat's somatic sensory cortex to peripheral stimuli.

OBSERVATIONS ON CORTICAL SOMATIC SENSORY MECHANISMS OF CAT AND MONKEY

OBSERVATIONS ON CORTICAL SOMATIC SENSORY MECHANISMS OF CAT AND MONKEY