|Year : 2006 | Volume
| Issue : 4 | Page : 233-235
"Mirror agnosia" in a patient with right occipitotemporal infarct
Bijoy K Menon, KR Shanbhogue, C Mutharasu, S Gopinathan, S Balasubramanian, Chandramohan, Jebasingh Y Kingsly, M Jawahar
Institute of Neurology, Madras Medical College, Chennai, India
K R Shanbhogue
Institute of Neurology, Madras Medical College and Govt. General Hospital, Chennai - 600 003
Source of Support: None, Conflict of Interest: None
| Abstract|| |
We report the clinical profile and investigation of K, a patient suffering from agnosia for the concept of "mirrors". Normal people rarely confuse a mirror image for the real image. Our patient 'K' has intact attention, memory and language with a left visual neglect with left hemianopia. When shown an object on his left with a mirror kept sagitally on his right, K grabs for the reflection and even gropes behind the mirror for it. Yet, when shown the mirror alone, he is able to tell that it is a mirror. Thus the concept of a 'mirror' is lost in the experimental paradigm. An explanation for mirror 'agnosia' is provided and recent controversies in the analysis of visuospatial functions in humans is highlighted.
Keywords: Mirror agnosia, neglect
|How to cite this article:|
Menon BK, Shanbhogue K R, Mutharasu C, Gopinathan S, Balasubramanian S, Chandramohan, Kingsly JY, Jawahar M. "Mirror agnosia" in a patient with right occipitotemporal infarct. Ann Indian Acad Neurol 2006;9:233-5
|How to cite this URL:|
Menon BK, Shanbhogue K R, Mutharasu C, Gopinathan S, Balasubramanian S, Chandramohan, Kingsly JY, Jawahar M. "Mirror agnosia" in a patient with right occipitotemporal infarct. Ann Indian Acad Neurol [serial online] 2006 [cited 2019 Oct 23];9:233-5. Available from: http://www.annalsofian.org/text.asp?2006/9/4/233/29207
The externally perceived world is divided into 'right and left', 'up and down', 'front and back', based on an abstract set of axes oriented in the three dimensional plane. The realization of these six aspects of the world is inherent in humans when they look at a mirror. A mirror reflects the world that is opposite to where it is kept, e.g., a mirror on the left reflects image of whatever is present on the right. As the image in a mirror is not congruent with that visual field and the realization of that image being part of the visual field directly opposite to it is inherent in humans, they realize that the image in the mirror is a 'mirror image' and not a real image. Thus the idea of a mirror is gained. This suggests that the concept of a 'mirror' must be a higher order function of the visual unimodal or the heteromodal cortex as it entails a cognitive reflection after the formation of visual images. A loss of this function is 'mirror agnosia'.
| Case Report|| |
K, a sixty-year-old right-handed male who is a sculptor by occupation, presented with sudden onset of giddiness and a tendency to sway and fall two months ago. On clinical examination, he was conscious and oriented with a Mini Mental Status Examination score of 23/28 (he was illiterate), normal attention, language, visual and verbal memory and an appropriate fund of knowledge. Lobar functions showed left homonymous hemianopia, left visual hemi neglect with visuospatial dysfunction as assessed by the Benton's line orientation test, significant constructional apraxia for two-dimensional drawings and three-dimensional objects, simultagnosia and optic ataxia. There was no directional or motor hypokinesia to the left and no tactile or auditory neglect. Rest of the lobar functions and corpus callosal tests were normal.
A mirror of size three feet by two feet was kept in the coronal plane in front of 'K'. He was able to recognize the mirror and even show his body parts like 'nose', 'ear' and 'eyes' in it, though his attention towards the left side of the mirror as viewed by him was impaired. On keeping the mirror to his right, he was again able to recognize it and point out body parts in it.
The mirror was then brought close to him, near the right shoulder tip and as he was looking into it, a pen was brought to his left in the plane of his nose and he was asked whether he could see the 'pen'. When K said 'Yes', he was asked to grab the pen. He reached for the pen in the mirror, started groping about inside the frame of the mirror and even reached for the pen behind the mirror. This is shown in [Figure - 1]. When asked where the pen was, he said, "it is there but I am not able to reach it". The experiment was repeated keeping the pen in different directions. The result was the same. The same experiment was then tried by keeping the mirror in front of 'K' and the 'pen' behind him. This time, he reached for the pen behind him.
After one month the same tests were repeated, but this time after a delay 'K' tried to reach for the real 'pen', though he directed his hand behind him when the 'pen' was actually to his left.
| Discussion|| |
'K' had an agnosia for the concept of 'mirror' in the experimental paradigm, though there was no mirror agnosia out of the paradigm when the mirror was kept in the coronal plane in front and in the saggital plane on the right. The agnosia for the mirror was in the non-neglected or the right half of the visual field function, which is cognitively normal otherwise. Thus 'K' had 'mirror agnosia' in the right visual field and a left visual neglect.
An interpretation for 'mirror agnosia' is that it is a specific consequence of the visual neglect itself. The patient looks at the mirror image in the normal non-neglected field on the right and thinks that since there is nothing on his left, what is seen in the mirror must actually be inside the mirror or behind it and must be real. This interpretation raises several questions. Is there a conscious rationalization on the part of the patient trapped in a hemi-neglected world? Are past experiences with a mirror forgotten in the background of normal memory tests? Does reaching for the pen behind the mirror mean that the patient now thinks that the mirror is a 'glass'? Is this a transient delusion?
Alternatively, 'mirror agnosia' may not be a consequence of neglect even though it is usually accompanied by it. Responding correctly to a mirror image requires creation of a dual representation or 'mental diplopia' and this must be a function of the unimodal visual association area or the heteromodal right parietal cortex. Compromise of this ability may result in 'mirror agnosia'.
After one month of follow-up the 'mirror agnosia' in 'K' disappeared and he now has 'mirror ataxia' with the left visual neglect still present.
Mirror ataxia is when a patient very clumsily grabs for the real object looking at its reflection in the mirror but is able to grasp the real object normally. 'K' reaches behind him for a pen, which is to his left after seeing its reflection in the mirror. This dysfunction is qualitatively different to what can be expected from optic ataxia.
'Mirror agnosia' is therefore not a consequence of neglect, but is due to a dysfunction of the right parietal cortex in creating multiple representations of the world, i.e., a "mental diplopia". This conclusion is arrived at based on the assumption that mirror agnosia is a more severe malfunction of visuospatial dysfunction when compared to 'mirror ataxia', as is evident in 'K' in whom there was a transformation from the former to latter over the follow-up period of one month though the left visual neglect persisted. Binkofski et al note that larger infarctions in the right tempero parieto occipital region are associated with 'mirror agnosia' and smaller ones with 'mirror ataxia', which supports our assumption. However in the same article, Binkofski et al also note a double dissociation between 'mirror agnosia' and 'mirror ataxia', suggesting that the former is due to the lesions in the right tempero parieto occipital junction around the superior sulcus where as the latter is due to lesions in the anterior and superior posterior parietal cortex and the anterior tip of the inter parietal sulcus.
CT brain in patient K as shown in [Figure - 2], shows a right occipito temporal infarct involving the right superior temporal sulcus with extension to the thalamus and midbrain. There are no follow up CT scans or MRI brain of the patient to show the evolution of lesions, though patient 'K' too showed a dissociation between 'mirror agnosia' and 'mirror ataxia' on follow-up and the CT lesions do confirm with Binkofski's findings.
The 'mirror agnosia' in 'K' is in contra distinction to 'mirror image agnosia' in which a patient is unable to discriminate between an object and its mirror image when both are presented together. The latter is a defect in visuospatial function due to a problem in aligning an object in its three dimensional co-ordinates. 'K' did not have a 'mirror image agnosia'
| Conclusion|| |
The experimental paradigm using mirrors demonstrates agnosia for mirrors in a patient with left visual neglect. The multiple dissociations that occur between mirror agnosia, mirror ataxia and visual neglect in patients with visuospatial dysfunction raises many questions regarding higher order visual processing, answers to which are not yet known.
| References|| |
|1.||Ramachandran VS, Altschuler EL, Hillyer S. Mirror agnosia. Proc R Soc Lond B 1997;264:645-7. [PUBMED] [FULLTEXT]|
|2.||Binkofski F, Buccino G, Dohle C, Seitz RJ, Freund HJ. Mirror ataxia constitute different parietal lobe disorders. Ann Neurol 1999;46:51-61. [PUBMED] |
|3.||Priftis K, Rulconi E, Umilta C, Zorzi M. Pure agnosia for mirror stimuli after right inferior parietal lesion. Brain 2003;126:908-19. |
[Figure - 1], [Figure - 2]
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