Disturbed perception of colours associated with localized cerebral lesions. By J. C. Meadows (From the National Hospital for Nervous Diseases, Queen Square, London WCIN 3BG) Brain 1974: 97; 615–632.
Cambridge
Acquired cerebral achromatopsia is, at best, rare and its existence denied altogether by many authorities: thus Sir Gordon Holmes writing in 1918 and basing his views on ‘a very large number of cases’ considered that ‘isolated loss or dissociation of colour vision is not produced by cerebral lesions’. John Meadows aims to draw attention to evidence that bilateral but relatively discrete brain lesions may in fact lead to impaired colour vision. In discussing patients with acquired cerebral achromatopsia, his focus is on loss or impairment of the ability to distinguish hues or perceive the brightness of colours. For affected individuals, the world is grey and some may struggle with everyday activities through their inability to distinguish colours. But confusion has crept into the literature as a result of failure to distinguish the symptom of colour loss from abnormalities found only on formal testing; inability to name rather than perceive colour; situations in which the relevance of colour for interpreting the nature of an object or scene is lost; and failure to recognize that lesions of the anterior visual pathway may result in selective loss of acuity for colour compared with a white target.
Starting with the case of McKay and Dunlop (The cerebral lesions in a case of complete acquired colour-blindness. Scot Med Surg J 1899; 5: 503–12), and accepting 14 other examples, Dr Meadows extracts the subtleties of the patients’ descriptions, often verbatim, that allow the distinction between cerebral achromatopsia and defective colour vision better explained by one or other of the ambiguities already listed. Thus, Bodamer's patient—‘speaking’ in 1947—describes everything as black and white as if sitting in the cinema: and Pallis's case feels that ‘my shirts all look dirty ... I have no idea what tie to wear ... I can tell peas and bananas only by their shape ... an omelette looks like a piece of meat ... when I open a jar I never know whether I will find pickles or jam’. To these John Meadows adds one description of his own. Following a stroke affecting the right cerebrum and resulting in right upper quadrantinopia, a 44-year-old customs inspector underwent vertebral arteriography and immediately after was aware of inability to recognize faces or colour, and with loss of topographical orientation, in the context of a bilateral superior altitudinal hemianopia. Six years later, he remains impaired through loss of topographical sense and failure to recognize familiar faces such that, when disguised by Dr Meadows in a doctor's white coat, he is unable to identify his wife until she speaks. ‘Everything looks grey’ and he cannot distinguish silver from bronze coloured coins of equivalent size and shape, or postage stamps of different value; he prunes live shoots (green) not dead (brown) stems; in the context of mild difficulty with memory, he cannot recognize or name colours, reverting most bright hues to the impression of black but sometimes guessing with greater accuracy. He performs slowly but accurately on the Ishihara plates and coloured card sorting but his performance on the Farnsworth–Mansell 100 hue test is dreadful (Fig. 1).
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What is immediately striking to John Meadows is the presence of upper quadrantic field defects, often bilateral, in the reported cases; none have lower altitudinal abnormalities. All but two cases also manifest the rare and bizarre symptom of prosopagnosia but motor and sensory deficits are infrequent and uninformative except in so far as they are not to be expected if, as Dr Meadows quickly concludes, achromatopsia depends on visual perceptive deficits specifically associated with lesions in the lower part of the striate cortex, rather than representing just the most severe component of what is nonetheless a general defect of vision (Fig. 2). That Holmes had not encountered many such cases is explained by the high probability that survival from a through-and-through missile injury of the lower occipital cortex sufficient to cause selective upper altitudinal field loss is less likely than for other posterior brain injuries, due to the high probability of severing the venous sinuses or collateral damage to the midbrain. Taking into account all reported cases of upper altitudinal field defect in which judgements can be made on colour vision, Dr Meadows estimates that 7 of 12 with upper field loss (complete or incomplete) had achromatopsia compared with 0 of 16 having inferior altitudinal field defects. Autopsy evidence supports this association of a colour defect with inferior occipital lesions, the three available reports describing lesions affecting the junction of the fusiform and lingual gyri bilaterally—Brodmann areas 18, 19 and probably 37.
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These cases have cerebral achromatopsia not colour agnosia or anomia. They complain of alteration in the coloured world or cannot report its varieties. That said, their performance on formal tests may vary depending on the extent of the deficits and the ability of the apparatus used to detect abnormalities of hue discrimination throughout the colour spectrum. In that respect, ordering the shades of the Farnsworth–Munsell test proves far more discriminating than separating colours widely dispersed on the colour spectrum as grouped on the Ishihara plates. The subtlety, and hence the rarity, of these cases lies in the requirement for a bilateral lesion that involves the lower part of the striate cortex but not so large as to destroy that tissue and cause absolute loss of vision. Whether a unilateral lesion can cause cerebral achromatopsia is less clear; and the lack of a bilateral field defect does not necessarily denote the absence of a bilateral lesion especially given the common blood supply of the visual cortex from the basilar artery. But, taking all the claims and evidence together, John Meadows thinks not: relative loss of colour acuity rather than a specific defect of colour perception is his preferred interpretation for claims of cerebral achromatopsia without a bilateral lesion.
Colour anomia is altogether different in its features and the disorganization of visual processing. Commonly part of the syndrome of alexia without agraphia, colour anomia can be understood as separating the colour appreciating ‘centre’ from that which encodes the names of colours. This syndrome usually follows occlusion of the left posterior cerebral artery, infarcting the left occipital cortex and the splenium of the corpus callosum. In this situation, behaviour in response to colour and slavish matching of hues are normal. Colour agnosia describes the error of not being able to assign colours to named objects or use colours as cues in everyday activities. Perhaps it results most frequently from lesions of the inferior parietal lobule. Writing at a time when the disconnectionist modelling of cerebral function was undergoing something of a renaissance, largely through the efforts of Norman Geschwind (see Disconnexion syndromes in animals and man. Brain 1965; 237–94: 585–644), Dr Meadows sees the three cerebral syndromes affecting colour, which may overlap, as interruptions in a neuronal chain commencing in both visual cortices and terminating in the left hemisphere language area, fibres from the striate areas reaching the occipitotemporal regions bilaterally and from there connecting to the inferior parietal lobule and the language areas of Wernicke and Broca (Fig. 3).
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That hue discrimination, face recognition and topographical orientation occur as a syndrome of lower bilateral striate cortical damage tells us that these behaviours share the need to detect infinite varieties of detail that are slight and subtle, defy verbal description and are not supported by cues from other sensory modalities. Of these, colour perception, being more elemental than face recognition in the visual hierarchy, is perhaps the least vulnerable, so most rarely encountered and then only when highly selective damage occurs immediately adjacent to the striate cortex. Dr Meadows notes that Semir Zeki has recently described columns of the prestriate monkey cortex that are selectively responsive to colour—V4 occupying the anterior bank of the lunate sulcus above and extending down to emerge vertically in the posterior bank of the inferior occipital sulcus. Is V4 damaged in humans with cerebral achromatopsia? The different anatomical folding of the simian and human occipital cortices removes the obvious objection that the colour cortex is placed laterally in the monkey and, hence, anatomically remote from the lesions that cause achromatopsia in man. The anatomy of V4 in monkeys does not of itself explain the association of cerebral achromatopsia with upper altitudinal field defects in the clinical context. However, the columnar organization of colour in V4 may account for the description by some patients that colours are uniformly tinted (gold or red in two cases described by Macdonald Critchley and Pierre Rondot, respectively) or unpleasantly bright, dazzling and with prolonged after-images, if cells dedicated to particular wavelengths are selectively damaged.
Semir Zeki himself considers the history of cerebral achromatopsia to be one of ‘facts dominated by concepts, of errors repeated and compounded, of evidence dismissed and forgotten, all in the service of vague doctrines of questionable origin and even more questionable value that were never established’ (A century of cerebral achromatopsia. Brain 1990; 113: 1721–77). Nineteenth century clinico-pathological correlations identified cerebral achromatopsia with lesions of the fusiform and lingual gyri, but considered these to reflect damage to a region involved generically in visual perception such that all aspects of the visual scene were necessarily contaminated along with the appreciation of colour. The evidence supporting functional disaggregation of the visual cortex into component parts specialized for colour, form and motion emerged from experimental studies in animals and, later, functional brain imaging in response to colour stimuli. But as Professor Zeki points out, the story begins with Verrey (Hémiachromatopsie droite absolue. Archives d’Ophthalmologie, Paris 1888; 8: 289–301) who summarized the position: ‘tout ceci nous montre combine de questions sont encore a résoundre dans ce domaine des localisations cérébrales et combine nous nous mouvons encore sur un terrain peu ferme. Cependent toute nouvelle contribution à cette étude a son importance pour l’édification de ce monument dont Charcot et ses élèves ont été les fondateurs, et c’est là ce qui m’a engagé à publier l’observation précedénte’ (All this demonstrates to us that there are many issues still to be resolved regarding cerebral localizations, and how much we are still on soft ground in this area. Nevertheless, any novel contribution to the study of cerebral localizations is of some importance towards the building of this monument, the foundations of which were laid down by Charcot and his collaborators; and this is what led me to publish the above clinical observation). And, in describing his experience and thoughts on cerebral achromatopsia, John Meadows follows that tradition.
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