Vishnu Swarup Kadaba
Neurogram Research Department
Naeemah Rahim
August 29th, 2021
Brain damage can lead to many different neurological disorders, the symptoms and signs of which vary drastically due to differences in the circumstances of the accident. One such case is that of Cerebral Achromatopsia, an impairment of colour vision, which is caused due to bilateral⁶ brain damage, i.e., distortion of both sides of the brain, resulting in degraded performance and cognitive ability¹¹, to the ventro-medial (area v4 of primary visual cortex specifically, crucial for visual object recognition¹²) occipital and temporal lobes.¹ A partial or total loss of colour vision perception is observed and may occur supplementarily with other cognitive or perceptual losses.² Most patients describe the experience as observing the world in ‘shades of grey’.⁹ It is also often confused with Congenital Achromatopsia, a hereditary disorder responsible for congenital low vision and abnormal visual behaviour¹³, but the underlying physiological deficits of the disorders are completely different as in the case of expressions of patients with cerebral achromatopsia as seeing the world in the ‘colour of grey’, while those with congenital achromatopsia have never had an experience of colour or ‘grey’.
Patients with Cerebral Achromatopsia often do not have any experience with diverse colours but can understand contrast, etc. For example, according to a study¹ conducted by Cowey et al. and Heywood et al. in order to verify the peculiar nature of cerebral achromatopsia, ‘several signs of chromatic processing persist in an achromatopsic subject who, despite his inability to tell colours apart, can still detect chromatic borders, perceive shape from colour, and discriminate the direction in which a striped pattern moves when the determination of direction requires the viewer to 'know' which stripes have a particular colour.’ This means that there is evidence of colour blindness with wavelength processing, therefore eliminating the possible explanation of the destruction of the pathway responsible for wavelength transmission and elaboration. This provides researchers with great insight for further research into the peculiar phenomenon.
The diagnosis for Cerebral Achromatopsia is done through the assessment of several tests such as the Farnsworth-Munsell 100-hue test (test of colour ordering)³, and the Ishihara plate test⁴ (a colour perception test) . A majority of those with the disorder who take the test fail the test(s) listed above.
Each case of achromatopsia is unique and conditioned by its own set of situations, so it is not clear whether incomplete achromatopsia, a milder form of the condition which allows comparatively more colour recognition, is merely a less severe form of the disorder or whether it is qualitatively different and reflecting impaired colour constancy.¹ However, in most of the cases, it is considered to be a consequence of cortical damage that arises through ischemia (restriction in blood supply to tissues) or infraction (tissue death) of a specific area in the ventral occipitotemporal cortex of humans⁵, an important part of the brain responsible for establishing connections between the visual world and high-level language brain regions.¹⁴
The disorder is often characterized and cited as to project our lack of knowledge in the field of colour and visual processing. As such, current research is focusing on learning more about the cortical area involved in color processing. Great strides are being made with respect to determining the involvement of the ventral occipital cortex in color processing⁸, determining evidence of color-specific processing in the human ventral occipital cortex.⁷
Jonathan I., a painter with Cerebral Achromatopsia, is, by far, the most famous instance of the disorder. His case was immortalized by a study conducted in "The Case of the Colorblind Painter", published by Oliver Sacks and Robert Wasserman.¹⁰The study expresses the experience that Jonathan I. goes through, starting with an injury leading to his loss of colour perception to his struggles of adapting to a world in ‘shades of grey’. He also finally expresses gratitude to his condition. The literary work also captures the psychological effects, trauma and symptoms in a brilliant manner. For example, here is an excerpt from the study depicting the world in Jonathan’s eyes:
‘He saw people's flesh, his wife's flesh, his own flesh, as an abhorrent gray; "flesh-colored" now appeared "rat-colored" to him. This was so even when he closed his eyes, for his preternaturally vivid ("eidetic") visual imagery was preserved but now without color, and forced on him images, forced him to "see" but see internally with the wrongness of his achromatopsia. He found foods disgusting in their grayish, dead appearance and had to close his eyes to eat. But this did not help very much, for the mental image of a tomato was as black as its appearance.’
Cerebral Achromatopsia is, quite evidently, a mysterious and mind-boggling disorder to consider and tackle. Colour blindness that is not due to defects in the retina and with effective wavelength processing does seem to be a very strange phenomenon. Still, much further research is required to be conducted for the betterment of those suffering from the condition and further our knowledge in the wonders of the world of visual perception.
Bibliography
¹ Cowey, A., & Heywood, C. A. (1997). Cerebral achromatopsia: colour blindness despite wavelength processing. Trends in cognitive sciences, 1(4), 133–139. https://doi.org/10.1016/S1364-6613(97)01043-7
² Kuyk T., Drane D. (1994). Cerebral achromatopsia: Seeing the world in shades of grey. (n.d.). American Academy of Optometry. https://www.aaopt.org/detail/knowledge-base-article/cerebral-achromatopsia-seeing-world-shades-grey
³ٰ Michael S. Beauchamp, James V. Haxby, Jonathan E. Jennings, Edgar A. DeYoe, An fMRI Version of the Farnsworth–Munsell 100-Hue Test Reveals Multiple Color-selective Areas in Human Ventral Occipitotemporal Cortex, Cerebral Cortex, Volume 9, Issue 3, April 1999, Pages 257–263, https://doi.org/10.1093/cercor/9.3.257
⁴ Crognale, M. A., Duncan, C. S., Shoenhard, H., Peterson, D. J., & Berryhill, M. E. (2013). The locus of color sensation: cortical color loss and the chromatic visual evoked potential. Journal of vision, 13(10), 15. https://doi.org/10.1167/13.10.15
⁵ Jaeger W, Krastel H, Braun S (December 1988). "[Cerebral achromatopsia (symptoms, course, differential diagnosis and strategy of the study). I]". Klinische Monatsblätter für Augenheilkunde (in German). 193 (6): 627–34. doi:10.1055/s-2008-1050309. PMID 3265459.
⁶ Bouvier SE, Engel SA (February 2006). "Behavioral deficits and cortical damage loci in cerebral achromatopsia". Cerebral Cortex. 16 (2): 183–91. doi:10.1093/cercor/bhi096. PMID 15858161.
⁷ Zeki S, Watson JD, Lueck CJ, Friston KJ, Kennard C, Frackowiak RS (March 1991). "A direct demonstration of functional specialization in human visual cortex". The Journal of Neuroscience. 11 (3): 641–9. doi:10.1523/JNEUROSCI.11-03-00641.1991. PMC 6575357. PMID 2002358.
⁸ Beauchamp MS, Haxby JV, Jennings JE, DeYoe EA (1999). "An fMRI version of the Farnsworth-Munsell 100-Hue test reveals multiple color-selective areas in human ventral occipitotemporal cortex". Cerebral Cortex. 9 (3): 257–63. doi:10.1093/cercor/9.3.257. PMID 10355906.
⁹ Jaeger W, Krastel H, Braun S (December 1988). "[Cerebral achromatopsia (symptoms, course, differential diagnosis and strategy of the study). I]". Klinische Monatsblätter für Augenheilkunde (in German). 193 (6): 627–34. doi:10.1055/s-2008-1050309. PMID 3265459.
¹⁰ Sacks, Oliver. "The Case of the Colorblind Painter". An Anthropologist on Mars. New York: Random House, 1995. 3-41.
¹¹ Schapiro, A. C., McClelland, J. L., Welbourne, S. R., Rogers, T. T., & Lambon Ralph, M. A. (2013). Why bilateral damage is worse than unilateral damage to the brain. Journal of cognitive neuroscience, 25(12), 2107–2123. https://doi.org/10.1162/jocn_a_00441
¹² Roe, A. W., Chelazzi, L., Connor, C. E., Conway, B. R., Fujita, I., Gallant, J. L., Lu, H., & Vanduffel, W. (2012). Toward a unified theory of visual area V4. Neuron, 74(1), 12–29. https://doi.org/10.1016/j.neuron.2012.03.011
¹³ Defoort-Dhellemmes, S., Lebrun, T., Arndt, C. F., Bouvet-Drumare, I., Guilbert, F., Puech, B., & Hache, J. C. (2004). Achromatopsie congénitale: interêt de l'électrorétinogramme pour le diagnostic précoce [Congenital achromatopsia: electroretinogram in early diagnosis]. Journal francais d'ophtalmologie, 27(2), 143–148. https://doi.org/10.1016/s0181-5512(04)96108-6
¹⁴ Jin Wang, Marc F. Joanisse, James R. Booth, Reading skill related to left ventral occipitotemporal cortex during a phonological awareness task in 5–6-year old children, Developmental Cognitive Neuroscience, Volume 30,2018,Pages 116-122,ISSN 1878-9293,https://doi.org/10.1016/j.dcn.2018.01.011.(https://www.sciencedirect.com/science/article/pii/S1878929317301494)
Question
Is Cerebral Achromatopsia a condition due to the degeneration/ damage to the retina?
Yes
No
Partially
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