Eye closure enhances dark night perceptions.

Stefan Brodoehl,Carsten M Klingner,Otto W Witte

doi:10.1038/srep10515

Abstract

We often close our eyes when we explore objects with our fingers to reduce the dominance of the visual system over our other senses. Here we show that eye closure, even in complete darkness, results in improved somatosensory perception due to a switch from visual predominance towards a somatosensory processing mode. Using a tactile discrimination task and functional neuroimaging (fMRI) data were acquired from healthy subjects with their eyes opened and closed in two environments: under ambient light and in complete darkness. Under both conditions the perception threshold decreased when subjects closed their eyes, and their fingers became more sensitive. In complete darkness, eye closure significantly increased occipital blood-oxygen-level-dependent (BOLD) activity in the somatosensory and secondary visual processing areas. This change in brain activity was associated with enhanced coupling between the sensory thalamus and somatosensory cortex; connectivity between the visual and somatosensory areas decreased. The present study demonstrates that eye closure improves somatosensory perception not merely due to the lack of visual signals; instead, the act of closing the eyes itself alters the processing mode in the brain: with eye closure the brain switches from thalamo-cortical networks with visual dominance to a non-visually dominated processing mode.

Highlights

We often close our eyes when we explore objects with our fingers to reduce the dominance of the visual system over our other senses
The present study demonstrates that eye closure improves somatosensory perception not merely due to the lack of visual signals; instead, the act of closing the eyes itself alters the processing mode in the brain: with eye closure the brain switches from thalamo-cortical networks with visual dominance to a nonvisually dominated processing mode
Eye closure in complete darkness resulted in an enhancement of tactile sensory sensitivity similar to that observed in light (Fig. 1, Table 1)

Summary

Introduction

We often close our eyes when we explore objects with our fingers to reduce the dominance of the visual system over our other senses. Vision enhances the perception of non-visual stimuli, most likely via a shift of spatial attention and crossmodal interactions[6] Visual deprivation, such as observed in prisoners of war over months and in healthy subjects over days, hours and minutes, improves specific aspects of tactile, auditory and gustatory perception[7,8,9]. We hypothesized that deprivation of visual signals, which was achieved by eye closure, would result in an improved processing within the somatosensory system, namely via an increased cooperation and processing of the sensory thalamus and somatosensory cortices To test this hypothesis the sensory perception thresholds was determined in 16 healthy subjects who had to alternately open and close their eyes

Methods

Results

Conclusion