Lesion - Effects of Brain Lesions

Effects of Brain Lesions

Studies show there is a correlation between brain lesion and language, speech, and category-specific disorders. However, lesions in Broca's and Wernicke's areas are not found to alter language comprehension.

Lesions to the fusiform gyrus often result in prosopagnosia, the inability to distinguish faces and other complex objects from each other.

Lesions to the visual cortex have different effects depending on the sub-area effected. Lesions to V1, for example, can cause blindness in different areas of the brain depending on the size of the lesion and location relative to the calcarine fissure. Lesions to V4 can cause color-blindness, and bilateral lesions to V5 can cause the loss of the ability to perceive motion.

Lesion in amygdala would eliminate the enhanced activation seen in occipital and fusiform visual areas in response to fear with the area intact. Amygdala lesions change the functional pattern of activation to emotional stimuli in regions that are distant from the amygdala.

Lesion size is correlated with severity, recovery, and comprehension.

In the Wisconsin Card Sorting Test with unilateral frontal or nonfrontal lesions, patients with left frontal lesions did more poorly but had high perseverative error scores. In right frontal and nonfrontal lesions are impaired but due to differences in patients. As a result, medial frontal lesions are associated with poor performance.

An impairment following damage to a region of the brain does not necessarily imply that the damaged area is wholly responsible for the cognitive process which is impaired, however. For example, in pure alexia, the ability to read is destroyed by a lesion damaging both the left visual field and the connection between the right visual field and the language areas (Broca’s Area and Wernicke’s area). However, this does not mean one suffering from pure alexia is incapable of comprehending speech -- merely that there is no connection between their working visual cortex and language areas -- as is demonstrated by the fact that pure alexics can still write, speak, and even transcribe letters without understanding their meeting.