Biomedical subjects

Oleg V Favorov

Publications and source records attributed to Oleg V Favorov.

4 recordsLinked to original sources

PubMed2006

Activation of cat SII cortex by flutter stimulation of contralateral vs. ipsilateral forepaws.

A distinguishing feature of SII cortex is that it receives substantial input from skin mechanoreceptors located on both sides of the body. It remains uncertain, however, if integration of bilateral inputs occurs mainly in those regions of SII that represent near-midline body regions or also occurs to a significant extent in those regions of SII that represent the distal extremities. This issue was addressed using extracellular microelectrode recordings in cat SII in combination with the method of optical intrinsic signal (OIS) imaging. Stimulation of the central pad of either the contra- or ipsilateral forepaw with a 25-Hz sinusoidal vertical skin displacement ("skin flutter") stimulus evoked a prominent OIS response ("activation") in an extensive anteroposterior sector of SII. In the anteriorly located SII region that yielded the maximal OIS response to stimulation of the contralateral central pad, neurons consistently possessed receptive fields that included the stimulated skin site. This "forepaw" SII region also exhibited significant although 75% weaker OIS activation in response to stimulation of the ipsilateral central pad. Stimulation of the central pads of either contra- or ipsilateral forepaws also evoked OIS activation in the posteriorly located 'hindlimb' region of SII--defined as the SII region comprised of neurons with receptive fields on the contralateral hindlimb. The OIS response to ipsilateral central pad stimulation was strongest in the posterior SII region that borders the suprasylvian fringe--a region in which neurons have very large, and frequently bilateral, cutaneous receptive fields. The results indicate that widespread regions within cat SII receive cutaneous inputs from the ipsilateral distal forelimb. It is suggested that the functional role of these ipsilateral inputs may be different in different SII regions.

Action Potentials↗

PubMed2005

Stimulus-dependent spatial patterns of response in SI cortex.

BACKGROUND: Recently we reported that vibrotactile flutter stimulation of a skin locus at different amplitudes evokes an optical response confined to the same local region of the primary somatosensory cortex (SI), where its overall magnitude varies proportionally to the flutter amplitude. In this report, we characterize the impact of the flutter amplitude on the spatial patterns of activity evoked within the responding SI region. RESULTS: In order to characterize the spatial pattern of activity within the responding SI region, images of the flutter-evoked SI optical response were segmented and analyzed with spatial frequency analysis. The analysis revealed that: (1) dominant spatial frequencies in the optical intrinsic signal emerge within the responding SI region within 3-5 sec of stimulus onset; (2) the stimulus-evoked activity is spatially organized in a form of several roughly parallel, anterior-posteriorly extended waves, spaced 0.4-0.5 mm apart; (3) the waves themselves exhibit spatial periodicities along their long axis; and (4) depending on the flutter stimulus amplitude, these periodicities can range from fine 0.15 mm "ripples" at 50 microm amplitude to well-developed 0.5 mm fluctuations at the amplitude of 400 microm. CONCLUSION: The observed spatiointensive fractionation on a sub-macrocolumnar scale of the SI response to skin stimulation might be the product of local competitive interactions within the stimulus-activated SI region and may be a feature that could yield novel insights into the functional interactions that take place in SI cortex.

Animals↗

PubMed2005

Amplitude-dependency of response of SI cortex to flutter stimulation.

BACKGROUND: It is established that increasing the amplitude of a flutter stimulus increases its perceived intensity. Although many studies have examined this phenomenon with regard to the responding afferent population, the way in which the intensity of a stimulus is coded in primary somatosensory cortex (SI) remains unclear. RESULTS: Optical intrinsic signal (OIS) imaging was used to study the evoked responses in SI of anesthetized squirrel monkeys by 25 Hz sinusoidal vertical skin displacement stimulation. Stimuli were 10 sec duration with a 50 sec inter-stimulus interval. Stimulus amplitude ranged from 50 to 400 microns and different amplitudes were interleaved. Control levels of activity were measured in the absence of stimulation, and used to compare with activation levels evoked by the different stimulus amplitudes. Stimulation of a discrete skin site on the forelimb evoked a prominent increase in absorbance within the forelimb representational region in cytoarchitectonic areas 3b and 1 of the contralateral hemisphere. An increase in stimulus amplitude led to a proportional increase in the magnitude of the absorbance increase in this region of areas 3b and 1 while surrounding cortex underwent a decrease in absorbance. Correlation maps revealed that as stimulus amplitude is increased, the spatial extent of the activated region in SI remains relatively constant, and the activity within this region increases progressively. Additionally, as stimulus amplitude is increased to suprathreshold levels, activity in the surround of the activated SI territory decreases, suggesting an increase in inhibition of neuronal activity within these regions. CONCLUSION: Increasing the amplitude of a flutter stimulus leads to a proportional increase in absorbance within the forelimb representational region of SI. This most likely reflects an increase in the firing rate of neurons in this region of SI. The relatively constant spatial extent of this stimulus-evoked increase in absorbance suggests that an increase in the amplitude of a 25 Hz skin stimulus does not evoke a larger area of SI neuronal activation due to an amplitude-dependent lateral inhibitory effect that spatially funnels the responding SI neuronal population.

Animals↗

PubMed2004

SINBAD: a neocortical mechanism for discovering environmental variables and regularities hidden in sensory input.

We propose that a top priority of the cerebral cortex must be the discovery and explicit representation of the environmental variables that contribute as major factors to environmental regularities. Any neural representation in which such variables are represented only implicitly (thus requiring extra computing to use them) will make the regularities more complex and therefore more difficult, if not impossible, to learn. The task of discovering such important environmental variables is not an easy one since their existence is only indirectly suggested by the sensory input patterns the cortex receives--these variables are "hidden". We present a candidate computational strategy for (i) discovering regularity-simplifying environmental variables, (ii) learning the regularities, and (iii) using regularities in perceptual and decision-making tasks. The SINBAD computational model discovers useful environmental variables through a search for different, but nevertheless highly correlated, functions of any kind over nonoverlapping subsets of the known variables, this being indicative of some important environmental variable that is responsible for the correlation. We suggest that such a search is performed in the neocortex by the dendritic trees of individual pyramidal cells. According to the SINBAD model, the basic function of each pyramidal cell is to (i) discover and represent one of the regularity-simplifying environmental variables and (ii) learn to infer the state of its variable from the states of other variables, represented by other pyramidal cells. A network of such cells--each cell just attending to representation of its variable--can function as a sophisticated and useful inferential model of the outside world.

Association Learning↗