bilateral spectrum

bilateral spectrum
   Also known as bilateral scotoma. The term bilateral spectrum comes from the Latin words bi (two), latus (side), and spectrum (image, apparition). It is used to denote a relatively rare fortification spectrum (i.e. a * scintillating sco-toma), occurring in the context of a *migraine aura, whose development is exactly synchronized in the two hemifields. As a result, the bilateral spectrum may present in the form of a single central or pericentral spectrum. Various types of bilateral spectra (including the * rainbow spectrum) were described in 1904 by the British neurologist Sir William Richard Gowers (18451915). Bilateral negative scotomata (i.e. regions of loss of vision) occasionally develop into transient * blindness. In those rare cases where the tactile cortex is affected as well, a total loss of body-sense (i.e. *acenesthesia) may be experienced. As the involvement of both hemifields in fortification spectra is extremely rare, and cannot be explained with recourse to current hypotheses involving the mediation ofthese phenomena in a single cerebral hemisphere, the British neurologist Oliver Wolf Sacks (b. 1933) notes that "The existence of such scotomata poses very difficult problems to those who postulate a local, unilateral process as the basis of migraine auras."
   References
   Gowers, W.R. (1904). Subjective sensations of sight and sound: Abiotrophy, and other lectures. Philadelphia, PA: P. Blakiston's Son & Co.
   Sacks, O. (1992). Migraine. Revised and expanded. New York, NY: Vintage Books.

Dictionary of Hallucinations. . 2010.

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