Cat Primary Somatosensory Cortex Research Articles

Response of neurons in primary somatosensory cortex of cat following prolonged exposure to strong sinusoidal mechanical stimuli

Psychophysical studies in humans have demonstrated adaptation of the mechanoreceptive submodalities of flutter and vibration after prolonged presentation of a strong adapting, or conditioning, stimulus. In our studies we recorded from single neurons in cat primary somatosensory cortex, and followed a paradigm in which the response of a single unit was measured before and after the presentation of a strong conditioning stimulus. Our findings show no adaptive response in the 30 sec period immediately after cessation of the conditioning stimulus, and suggest that other parallel ascending pathways or somatosensory cortical areas other than SI account for these psychophysical observations.

Responses of neurons in cat primary somatosensory cortex to repetitive stimulation of vibrissae

Extra- and intracellular responses of neurons in the primary somatosensory cortex to repetitive mechanical stimulation of the vibrissae at different frequencies were studied in unanesthetized curarized adult cats. Unlike responses to electrical stimulation of the combined afferent input (the infraorbital nerve) spike discharges of neurons in response to vibrissal stimulation can reproduce rather higher frequencies of stimulation and their initial character changes more often in the course of the repetitive series. Most cortical neurons were characterized by limitation of the area of their peripheral receptive fields with an increase in the frequency of adequate repetitive stimulation. A group of cortical neurons was distinguished by its ability to respond to high-frequency stimulation and to generate burst discharges. Comparison of the frequency characteristics of spike responses of these cells and of inhibitory synaptic action in other cortical neurons led to the conclusion that this group of cells thus distinguished may be inhibitory cortical neurons. The role of interaction between excitatory and inhibitory processes arising in cortical neurons during repetitive stimulation of different areas of their receptive fields is discussed.

Responses of somatosensory cortical neurons to inhibitory amino acids during topical and iontophoretic application of epileptogenic agents

Single unit activity in cat primary somatosensory cortex (layers IV–VI) with contralateral forelimb receptive fields was recorded extracellularly via compound multi-barrelled micropipettes with simultaneous iontophoresis of amino acids. Units exhibited inhibitory responses to γ-aminobutyric acid (GABA), β-alanine (ALA), and l-glycine (GLY). The order of potency was GABA > ALA > GLY. Excitatory responses to d,l-homocysteic acid (HC) and l-glutamate (GLU) were observed. HC was more potent than GLU. In topical penicillin, bicuculline, or strychnine foci units, at the depth studied (1–2 mm), had HC-induced interburst activity which was normally responsive to GABA, ALA or GLY. This occurred despite obvious epileptic involvement of the unit in a bursting firing pattern associated with paroxysmal electrocorticogram (ECoG) discharges. Unit bursts proved to be completely resistant to the exogenous inhibitory amino acids applied by iontophoresis. Iontophoretic application of bicuculline (100 nA) antagonized neuronal responses to GABA and ALA without effect on GLY. Strychnine (100 nA) antagonized responses to GLY and ALA, without effect on GABA. A comparison of topical and iontophoretic results indicated failure of topical epileptogenic agents to consistently diffuse in adequate concentration into deeper cortical layers (IV–VI) to produce characteristic receptor antagonism. The iontophoretic application technique was consequently selected as the most appropriate method for further study of the effects of penicillin iontophoresis on responses of deep cortical neurons to amino acids.

Sensory hind-limb representation in Sml cortex of the cat. A unit analysis

A unit analysis was made of mechanoreception in the hind limb area of the cat primary somatosensory cortex, SmI. A sample of 588 units was studied in this area. Eighty per cent of the units were influenced by light mechanical peripheral stimulation of the contralateral hind limb; the remainder were not influenced by any form of mechanical stimulation. No ipsilateral representation was found. Most excitable units were situated in the middle cortical layers. All were characterized by static lemniscal properties, i.e., short latency, and also place as well as modality specificity. These units were distributed with a somatotopic organization. Excitable units which could be defined in terms of adaptive property and adequate stimulus were classified as hair, touch, tap, pressure or joint. The representation of slowly-adapting joint receptors was slight, and there was no evidence for the representation of muscle stretch receptors or Golgi tendon organs. The submodalities which were represented were topographically distributed in caudomedial to rostrolateral gradients of epidermal and subepidermal receptors. This distribution appears to be correlated with the cortical architecture.

OBSERVATIONS ON CORTICAL SOMATIC SENSORY MECHANISMS OF CAT AND MONKEY

OBSERVATIONS ON CORTICAL SOMATIC SENSORY MECHANISMS OF CAT AND MONKEY