Visuo-spatial imagery in dreams of congenitally and early blind: a systematic review

Abstract

BackgroundThe presence of visual imagery in dreams of congenitally blind people has long been a matter of substantial controversy. We set to systematically review body of published work on the presence and nature of oneiric visuo-spatial impressions in congenitally and early blind subjects across different areas of research, from experimental psychology, functional neuroimaging, sensory substitution, and sleep research.MethodsRelevant studies were identified using the following databases: EMBASE, MEDLINE and PsychINFO.ResultsStudies using diverse imaging techniques and sensory substitution devices broadly suggest that the “blind” occipital cortex may be able to integrate non-visual sensory inputs, and thus possibly also generate visuo-spatial impressions. Visual impressions have also been reported by blind subjects who had near-death or out-of-body experiences.ConclusionDeciphering the mechanistic nature of these visual impression could open new possibility in utilization of neuroplasticity and its potential role for treatment of neurodisability.

Mental Imagery in Dreams of Congenitally Blind People

“…Nonetheless, over the years, it has been reported that congenitally blind people can, and do, experience oneiric visuo-spatial imagery in a way that is similar to sighted individuals [5,[41][42][43]. In keeping with this, significant negative correlations between the visual activity index (defined by performing a quantitative analysis of dream content, also see [42]) and occipital alpha power have been demonstrated during REM's dream mentation in congenitally blind subjects [43].…”

“…More recently, it has been suggested that vividness of dream experiences, including experience of colours, may predominantly depend on the intensity of the brain activity in distinct neurocircuitry [57]. However, how distinct anatomical and physiologic processes of the congenitally blind brain may affect this process remains an important unanswered question, with some initial insights gained from neuroimaging studies (for further in-depth systemic review, please refer to [5]).…”

“…Arguably, sensory modalities other than vision (e.g., auditory, haptic/tactile, and olfactory) enable adaptive functional development of the occipitotemporal visual system in the absence of visual stimulation early in life [18][19][20][21][22][23][24][25][26][27]. This model is supported, at least prima facie, by evidence of cross-modal neuroplasticity of the "blind visual cortex" and its involvement in episodic memory [28], language [18], and in auditory [21,22,27,29] and haptic [30] processing [5].…”

“…More recently, it has been shown that individual sensitivity to a particular sensory input may underlie that person's sensory imagery deficits [1]. 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].…”

“…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.…”