Rapid eye movements are reduced in blind individuals

Abstract

There is ongoing controversy regarding the role of rapid eye movements (EMs) during rapid eye movement (REM) sleep. One prevailing hypothesis is that EMs during REM sleep are indicative of the presence of visual imagery in dreams. We tested the validity of this hypothesis by measuring EMs in blind subjects and correlating these with visual dream content. Eleven blind subjects, of whom five were congenitally blind (CB) and six late blind (LB), and 11 matched sighted control (SC) subjects participated in this study. All participants underwent full‐night polysomnography (PSG) recordings that were staged manually following American Academy of Sleep Medicine (AASM) criteria. Nocturnal EMs were detected automatically using a validated EM detector, and EM activity was represented as “EM coverage” computed as percentage of time with EM in each sleep stage. Frequency of sensory dream elements was measured in dream recall questionnaires over a 30‐day period. Both blind groups showed less EM coverage during wakefulness, N1, N2 and REM sleep than did controls. CB and LB subjects did not differ in EM activity. Validation of the detector applied to blind subjects revealed an overall accuracy of 95.6 ± 3.6%. Analysis of dream reports revealed that LB subjects reported significantly more visual dream elements than did CB. Although no specific mechanisms can be revealed in the current study, the quasi absence of nocturnal EMs in LB subjects despite preserved visual dream content does not support the visual scanning of dreams hypothesis. Specifically, results suggest a dissociation between EMs and visual dream content in blind individuals.

Nocturnal eye movements in patients with idiopathic rapid eye movement sleep behaviour disorder and patients with Parkinson’s disease

“…A dominating hypothesis for the presence of EMs in sleep is the scanning hypothesis stating that we scan our dream scenes by involving the visual cortex (Dement & Kleitman, 1957;Roffwarg, Dement, Muzio, & Fisher, 1962). The presence of EMs in active sleep depends on earlier and maintained presentation of visual sensory information, as seen from the fact that congenitally blind subjects and those who develop blindness later in life show almost an absence of EMs in active sleep (Aubin et al, 2018;Christensen et al, 2019 The EM coverage in wakefulness between lights off and on is likely to reflect both rapid EMs (also referred to as saccades) during nocturnal wake periods and the wake period between lights off and sleep onset, as well as the drifting of the eyes (slow EMs) typically seen in the short transition period from wakefulness to sleep onset.…”

“…A dominating hypothesis for the presence of EMs in sleep is the scanning hypothesis stating that we scan our dream scenes by involving the visual cortex (Dement & Kleitman, 1957; Roffwarg, Dement, Muzio, & Fisher, 1962). The presence of EMs in active sleep depends on earlier and maintained presentation of visual sensory information, as seen from the fact that congenitally blind subjects and those who develop blindness later in life show almost an absence of EMs in active sleep (Aubin et al., 2018; Christensen et al., 2019). Consequently, EMs are dependent on a complex network interaction between visual cortical and brainstem areas.…”

On Moving the Eyes to Flag Lucid Dreaming

“…Despite the fact that congenitally blind individuals do not experience "visual" dreams and display rapid eye movements (Gross et al, 1965;Kerr et al, 1982), a recent work found that the frequency of their gazes is reduced and bears no relation with dream content (Christensen et al, 2019). In cats, when the visual cortex is removed the rapid eye movements are preserved (Jouvet, 1962), and the PGO waves, which may induce the formation of the images and other visual aspects of dreams, are generated simultaneously and in parallel with the rapid eye movements (Vanni-Mercier and Debilly, 1998).…”

Mental Imagery in Dreams of Congenitally Blind People

“…In dreams, (oneiric) imagery is thought to arise from the reactivations and manipulations of sensory cortical representations during sleep, although the exact nature of these mechanisms remains uncertain [3][4][5]. Perhaps unsurprisingly, the presence of visual imagery in the mentation of dreams of congenitally blind people has long been a matter of significant controversy [5][6][7][8][9][10][11][12][13][14][15][16]. To date, it is unclear to what extent the absence or loss of vision affects the sensory and pictorial sensitivity for dream construction [15,17], or, more specifically, how it impacts the ability of the nervous system to integrate sufficient sensory information to produce mental images during dreaming.…”

“…In turn, this may also ensure attentional shifts that 'reset' mnemonic processing frames and enable oneiric conscious experiences [39], including discrete epochs of the generation of visual-like mental representations during REM sleep [3,37,40]. With this background, it is of note that congenitally blind people show significantly reduced, or fully absent, rapid eye movements during sleep [8].…”