A disorder of colour perception associated with abnormal colour after-images: a defect of the primary visual cortex.
A 64 year old woman with posterior cortical atrophy secondary to probable Alzheimer's disease is described. Her presenting symptom was of seeing objects as abnormally coloured after prior exposure to a coloured stimulus. Formal testing disclosed that the patient experienced colour after-images of abnormal latency, duration, and amplitude.The demonstration of prolonged colour after-images in a patient with a cortical disease process provides strong evidence that the generation of colour after-images is mediated at least in part by the visual cortex. A mechanism for the generation of colour after-images is proposed in which abnormal prolongation of the images results from excessive rebound inhibition of previously excited wavelength selective neurons in V1. This may occur as a consequence of the relative sparing of inhibitory interneurons in V1 in the context of the degeneration of excitatory neurons that occurs in Alzheimer's disease.
Chan
D
D
Dementia Research Group, Department of Clinical Neurology, Institute of Neurology, Queen Square, London WC1N 3BG, UK. d.chan@dementia.ion.ucl.ac.uk
Crutch
S J
SJ
Warrington
E K
EK
D000360:Afterimage / Q000502:physiology*; D000544:Alzheimer Disease / Q000175:diagnosis / Q000503:physiopathology*; D001284:Atrophy; D002470:Cell Survival / Q000502:physiology; D003118:Color Perception / Q000502:physiology*; D003119:Color Perception Tests; D003117:Color Vision Defects / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D014793:Visual Cortex / Q000473:pathology / Q000503:physiopathology*