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A lesion is any abnormality in the tissue of an organism (in layman's terms, "damage"), usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury. Within psychology the term brain lesion is used with specific reference to experimentally induced damage to animal brains for research purposes
DuVerney was the first to use experimental ablation method on animals in 1679. Flourens first published the method in 1824, describing the method and behavioral effect of brain damage.
Lesions done by knife cuts and suction techniques, called mechanical lesions, were tried by Veyssiere and Nothnagel in 1874. This process was done by inserting a fine wire blade through the head, rotating the curved or angled wire, and cutting neural projection. Baginski and Lehmann used this method with thin glass tube lowered through a small hole in the skull in 1886.
In 1895, Golsinger was the first to make electrolytic lesions in animals. In 1898 Sellier and Verger destroyed discrete areas in the caudate and anterior segment of internal capsule by passing current through double-needle insulated electrodes. This process kills neurons surrounding the electrodes.
In 1908, Horsley and Clark developed the stereotaxic method and combined it with electrolytic lesions to improve localization, precision, and reliability of brain damage in subcortical structures.
Lesions are caused by any process that damages tissues. Lesions can also be caused by metabolic processes, like an ulcer or autoimmune activity, as in the case with many forms of arthritis.
Note that lesions are not limited to animals or humans; damaged plants are said to have lesions.
Studies show there is a correlation between lesion in the brain and language, speech, and category-specific disorders. However, lesions in Broca's and Wernicke's areas are not found to alter language comprehension.
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.
Lesions or ablation in psychology or an ablation experiment or lesion experiment is the removal of tissue to explore its function and was a basic research methodology in physiological psychology in the earlier part of the 20th century. The approach was refined in 1824 by Marie Jean Pierre Flourens, a French physiologist.
Ablative brain surgery
Ablative brain surgery is also often used as an research tool in neurobiology. For example, by ablating specific brain regions and observing differences in animals subjected to behavioral tests, the functions of the removed areas may be inferred.