E.V. Loseva – Dr.Sc. (Biol.), Chief Research Scientist, Laboratory of Functional Neurocytology,  Institute of Higher Nervous Activity and Neurophysiology of RAS (Moscow)

E-mail: losvnd@mail.ru 

N.A. Loginova – Ph.D. (Biol.), Senior Research Scientist, Laboratory of Functional neurocytology, 

Institute of Higher Nervous Activity and Neurophysiology of RAS (Moscow)

E-mail: nadezhda.loginova1982@gmail.com

V.V. Gavrilov – Ph.D. (Psychol.), Senior Research Scientist, Laboratory of psychophysiology,  Institute of Psychology of RAS (Moscow); 

Senior Research Scientist, Institute of Experimental Psychology under Moscow State University  of Psychology and Education

E-mail: nvvgav@mail.ru

It is known that early sensory deprivation elicits compensatory neural plasticity and changes in behaviour. Morphometric studies of neocortical cytoarchitectonic after long-term visual deprivation could shed light on its effects on the organization of neural activity. The aim of this study was to analyze the thickness of cortical layers in different brain areas in rats with an intact visual system raised in conditions of total darkness (experimental group) and in conditions of natural lighting (control group). We prepared 18-20 µm frontal plane serial slices of motor (a.3.20), retrosplenial posterior (p.4.52), auditory (p.4.52), somatosensory (p.4.52) and primary visual (p.7.30) areas of the cortex in 3-month-old Long-Evans rats (experimental group, n=8; control group, n=8). The slices were stained with Nissl’s method with the subsequent lighting procedure through alcohol of increasing concentrations. Three slices from each level were taken into analysis. Selected slices were photographed (Axioplan-2, Germany) with 50-fold amplification and analyzed with ImageJ program. Statistical comparisons were made using Mann-Whitney U test for independent samples.

The significant changes were observed in all layers of primary visual cortex, as well as motor cortex, except layer 1; in the 2-3rd and 5th layers of auditory cortex; in the 1st, 2-3rd and 5th layers of somatosensory cortex and in the 4th and 6th layers of retrosplenial cortex.

Thus, despite the accepted view that sensory deprivation in one modality is usually compensated by an increased involvement of other modalities, our results show that this is not always the case. Early visual deprivation in our study was associated with a decreased thickness of layers not only in visual cortex but also in other sensory brain areas, i.e. somatosensory and auditory. Rats raised in the conditions of total darkness also displayed decreased motor activity. Visual deprivation and decreased motor activity in early development could account for the formation of a significantly smaller behavioural repertoire, which was associated with decreased thickness of cortical layers. We suppose that these morphometric data taken together with electrophysiological measures of brain activity in behaving animals could assist in a deeper understanding of the role of vision in the organization of behavior and formation of individual experience.

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