Hebbian plasticity

Primary sensory areas in the vertebrate neocortex (visual, auditory, somatosensory) is a central region of corresponding sensory analyzer. It was considered for a long time that such regions provide exact coding if visual information and thus doesn't undergo plasticity. However, several types of learning have been found there including perceptive learning that is accompanied by plastic restructurings in primary sensory areas. A bright example of such a learning is an ability to distinguish close audotory tones that is developed during prolonged musical lessons. The employees of the IHNA RAS have published a paper about cellular mechanisms of plasticity in the primary visual cortex of mice. They showed that besides the Hebbian learning so called heterosynaptic plasticity also takes place. The main idea of heterosynaptic plasticity is to modification of synapses exclusively caused by the activity of postsynaptic neuron when the presynaptic one is not active. In our research we have studies change of functional properties of neurons inside the visual cortex after induction of high-frequency bursts of action potential (intracellular tetanization). This was shown earlier that such an interaction results to massive restructurings of synaptic inputs to a given neuron where some inputs undergo long-term potentiation and another ones exhibit long-term depression. In order to be able to selectively activate a single cell we used optogenetics approach where all cells were infected by adeno-associated virus that has brought gene of light-activated channel protein called rhodopsin 2. After that a thin glass electrode was introduced to the neuron that allowed both to register extracellular activity and to light this cell locally by blue light inducing high-frequency bursts of spikes there. At the beginning of the experiment 12 gratings moving in different directions were demonstrated to a mouse. Next, the responses of the neurons were used to construct so called orientation selectivity map of the cells. Neurons in the primary visual cortex doesn't respond to all visual stimuli in the same way. They respond stronger only to a stimulus of some optimal orientation. Higher the difference between the responses to different moving stimuli narrower the orientation tuning of the cell. This was shown that induction of high-frequency (75-100 Hz) bursts of spikes in pyramidal neuron broadens its orientation selectivity. Using these data one can suppose that high-frequency spiking activity occured in the post-synaptic cell in the absence of specific sensory stimulation (i.e., during the sleep) can result to decline in the directional selectivity of cells that provides an opportunity to the more thin adjustment of properties of the visual cells to new visual scenes during the alert state. The probable mechanism underlying in such restructurings is based on change in effectiveness of synaptic inputs developing through the mechanism of heterosynaptic plasticity. Such an investigation was supported by the Russian scientific Foundation (grant No. 20-15-00398).