Cognitive Brain Research 15 2003 277 284 www elsevier com locate cogbrainres Research report Visual dream content graphical representation and EEG alpha activity in congenitally blind subjects Teresa Paiva Lara Pessoa Tiago Mestre Raquel Marques Rosa Santos Helder Bertolo EEG Sleep Laboratory Centro de Estudos Egas Moniz Faculdade de Medicina de Lisboa Hospital Santa Maria 1600 Lisbon Portugal Accepted 11 July 2002 Abstract It is currently claimed that congenitally blind do not have visual imagery and are therefore unable to present visual contents in their dreams The aim of our study was to quantitatively evaluate the existence of visual imagery in born blind dreams and to correlate it with objective measures such as sleep EEG frequency components namely with alpha attenuation regarded as an indicator of visual activity and graphical analysis of dream pictorial representations The investigation was carried out via simultaneous recordings of dream reports and polysomnography during nocturnal sleep at volunteers homes scheduled regular awakenings during the night provided the data for dream and EEG analysis In the morning subjects were asked to make a drawing of their dream images Congenitally blind n510 were comparable to normal sighted subjects n59 the two groups presented equivalent visual activity indices and no differences in the analysis of graphical representation of dreaming imagery However blind subjects presented a lower rate of dream recall than sighted 27 versus 42 Both groups had significant negative correlation between Visual Activity Index VAI and alpha power in the central and occipital O2 derivations blind C4 r520 615 P 0 005 O2 r520 608 P 0 006 sighted C4 r520 633 P 0 01 O2 r520 506 P 0 05 This correlation was weaker for the blind in O1 r520 573 P 0 05 and non existent for the sighted Blind individuals have significantly lower alpha activity in the central derivation In conclusion the congenitally blind have visual content in their dreams and are able to draw it and as expected their VAI is negatively correlated with EEG alpha power 2002 Elsevier Science B V All rights reserved Theme Neural basis of behaviour Topic Biological rhythms and sleep Keywords Dreams Visual imagery Congenitally blind Alpha activity 1 Introduction It is open to discussion whether congenitally blind subjects have dreams with visual imagery content and if they do whether this ability represents images capable of being represented graphically Since for sighted subjects the dreaming experience is associated with visual activity it used to be widely thought that blind persons do not dream This was strongly refuted by several authors and it is nowadays accepted that the dreams of the blind are vivid and self engaging 16 38 40 Furthermore it is currently accepted that the congenitally blind or those who lose their sight before the age of 5 or 7 have dreams without Corresponding author Tel 1351 1 799 0610 fax 1351 1 7805642 E mail address helderbertolo netcabo pt H Bertolo visual content 40 Some authors also report that subjects who are born blind report dreams which do not include any description of scenes or landscapes but contain mostly sounds touch sensations or emotional experiences 34 37 44 Laboratory dream data obtained for 10 blind subjects showed that blind and normal dreams were identical except for two congenitally blind subjects whose dreams did not have visual components 41 This knowledge may however be questioned In several studies involving visual imagery the congenitally blind showed only slight differences in performance when compared with sighted subjects 2 4 14 47 64 the blind may employ other strategies to solve the problems posed experimentally Spatial knowledge and metric properties seem to be preserved in congenitally blind subjects 29 In pictorial and spatial representations of two and threedimensional matrices of differing complexity the congeni 0926 6410 02 see front matter 2002 Elsevier Science B V All rights reserved PII S0926 6410 02 00199 4 et al Cognitive Brain Research 15 2003 277 284 H Bertolo 278 tally blind only perform worse than sighted subjects in the latter 12 13 A psychological study conducted on subjects born blind indicates that they have capabilities to generate visuo spatial images 61 Dream content analysis is open to many criticisms due mainly to subjectiveness Nevertheless Hall and Van de Castle have proposed a highly reproducible index that is widely used in dream content analysis 30 None of the studies mentioned previously used this classification system A fundamental difficulty of assessing whether dreams with visual content occur in the congenitally blind is the lack of accepted objective physiological measures One possibility is to use recordings of Rapid Eye Movement episodes REMs that are related to visual exploration 32 36 Some authors did not record REMs in blind subjects this led them to conclude that the blind do not have visual content in their dreams 7 Recent studies which describe rapid eye movements during blind persons dreams have refuted this however 39 Furthermore it is known that there are correlations between EEG and visual activity Some authors regard alpha activity attenuation or blocking as an indicator of visual imagery in general 6 11 28 57 62 63 Alpha power was lower in the right hemisphere when subjects performed an imaginative block rotation task and was suppressed when subjects either watched or played Pong TV tennis 50 watching Pong was as effective as playing the game in producing alpha asymmetry in the parietal region but motor involvement enhanced asymmetry at central and temporal leads EEG frequency bands are correlated with visual imagery and abstract thought and the alpha power is more affected by visual mentation than by abstract mentation 45 46 Parietooccipital alpha activity was suppressed strongly while subjects visualized and evaluated letters but forming a visual image caused less suppression than did direct inspection of the imaged pattern 56 Magnetoencephalographic studies have also shown a dampening of the alpha activity within 200 ms after the appearance of a visual stimulus and also during visual imagery 31 Taking this information into consideration we analysed EEG alpha power in congenitally blind subjects as a possible indicator of the visual content of their dreams We also checked for differences regarding the correlations between occipital derivations O1 and O2 and central derivations C4 Finally we