The response of neurons to natural stimulation depends on the past history of stimulation. Sensitivity increases during periods of weak stimulation, whereas when the background stimulation is strong the sensitivity is reduced. This form of gain control is called sensory adaptation. Our research is focused on the mechanisms of adaptation in the cortex and the thalamus. We have found that cortical adaptation is highly specific to the stimulated whisker and thus indicate that inputs from different whiskers undergo independent adaptation paths. We also study how adaptation affects the balance between excitation and inhibition. Our data provide direct indication for faster adaptation rate of inhibition, when compared to excitation.
It was recently discovered that subthreshold membrane potential fluctuations of cortical neurons can precisely repeat during spontaneous activity, seconds to minutes apart, both in brain slices and in anesthetized animals. These repeats, also called cortical motifs, were suggested to reflect a replay of sequential neuronal firing patterns. We searched for motifs in spontaneous activity, recorded from the rat barrel cortex and from the cat striate cortex of anesthetized animals, and found numerous repeating patterns of high similarity and repetition rates. To test their significance, various statistics were compared between physiological data and three different types of stochastic surrogate data that preserve dynamical characteristics of the recorded data. We found no evidence for the existence of deterministically generated cortical motifs. Rather, the stochastic properties of cortical motifs suggest that they appear by chance, as a result of the constraints imposed by the coarse dynamics of subthreshold ongoing activity.
Using dual intracellular recordings it was previously shown that the membrane potential of nearby cortical cells in the visual cortex of anesthetized cats is highly synchronized. Similar behavior is found in the barrel cortex of the rat. We utilize this technique to investigate the real-time relation between excitation and inhibition during ongoing activity and during sensory evoked response. Our recently obtained data indicate that the excitatory network is under continuous control of inhibition.