Electrophysiological expression of quick activation of cat's cortex by acoustic stimuli
Petrek, J.; Lisonĕk, P.
Acta Universitatis Palackianae Olomucensis Facultatis Medicae 116: 81-96
1987
ISSN/ISBN: 0301-2514 PMID: 2962467 Document Number: 290197
The present material together with the data from our earlier papers as well as the work by other authors allows the following summarization: 1. Acoustic impulses arrive practically simultaneously to the primary projection area and also to the cells in the other areas of cat's brain cortex. The approximately equal latency of the onset of the main positive wave of acoustic SNPR and PR at low intensities of the stimulus bear out this conclusion. The difference in the shape of the two responses and in latency of the peaks of main positivity and negativity of acoustic SNPR and PR are probably due to the different distribution of afferent fibres in primary and extraprimary regions. The differences in cytoarchitectonics of the two regions has undoubtedly also its share in it and so has the unequal organization of intracortical interconnection in them. 2. We admit that although the problem has not been solved so far by experiments, part of the acoustic messages reach the cells in the extraprimary cortical areas even earlier than the cells in the primary cortical area. The low voltage positive-negative complex (P0, N0) preceding the acoustic SNPR could be an electrophysiological expression of this early activation, but if it is not a part of far-field recorded acoustic brain stem response. 3. Amplitude characteristics of acoustic SNPR show that the anterior part of the middle suprasylvian gyrus and the upper part of the anterior suprasylvian gyrus are activated by acoustic messages in the most massive way of all extraprimary areas. Morphological basis for the quick activation of neurons of the suprasylvian area is undoubtedly formed by the system of direct connections established between neurons of the suprasylvian area of cat's brain cortex and some diencephalic and mesencephalic structures taking immediate part in the reception and transmission of acoustic information. 4. Cortical acoustic SNPR as well as PR result from the activity of the common specific thalamocortical system, which brings acoustic messages into both cortical areas of cat's brain simultaneously. The common subcortical origin of acoustic SNPR and PR explains well a number of common electrophysiological characteristics of these two types of cortical responses. We remind some of them. The main components of acoustic SNPR and PR registered in waking animals after anaesthesia with Nembutal or chloralose change in the same way: in both the amplitude of the main components increases and their latency is prolonged in dependence on the depth of the anesthesia. In freely moving animal but also in animal anaesthetized with Nembutal the amplitude of both main components of acoustic SNPR and PR shows the same dependence on the changing level of excitability of the central nervous system: an increase in amplitude integral of the EEG is accompanied by an increase in amplitude of positivities and negativites of both responses. Analogically during prolonged rhythmic stimulation the amplitude of the main components of acoustic SNPR and PR changes in the same way. The recovery curves of the first positivities and negativities of the acoustic SNPR and PR have practically the same dynamics in freely moving cat as well as in cat anaesthetized with Nembutal. 5. Cortical acoustic SNPR unlike classical association responses (AR) is not the result of an activity of polysensory systems of the central nervous system. This conclusion is in good agreement with the results of study of interaction between cortical SNPR to acoustic and somatosensory stimuli in the anterior part of the suprasylvian gyrus. On the basis of above-mentioned it can be concluded that the primary projection area as well as extraprimary areas of cat's brain are activated simultaneously by means of a common specific subcortico-cortical system. SNPR is an electrophysiological expression of this activation. The main functional importance of quick activation of nonprimary areas, however, remains unclear so far, even though some present findings point out that each extraprimary area participates in its own way in the reception and processing of acoustic information and thus also in the formation of the final behavioural response of the organism in a given moment.