BILATERAL HALLUCINATION

   Also known as bilateral auditory hallucination. Both expressions are indebted to the Latin words bi (two) and latus (side). The term bilateral hallucination translates roughly as 'two-sided hallucination'. The term is used mainly with reference to hallucinations occurring in the auditory modality. In a loose sense, it is used to denote an * auditory hallucination subjectively localized as coming either from both sides of the head, or from an indefinite location. In a more restricted sense, the term bilateral hallucination has been used since the late 19th century to denote an auditory hallucination that has a different quality and/or content for each side of the head. Thus the affected individual may hear pleasurable and encouraging voices in the right ear, and abusive, threatening voices in the left ear. Or the affected individual may hear a female voice in the right ear, and a male voice in the left. The French alienist Jacques Joseph-Valentin Magnan (1835-1916) considers bilateral hallucinations in the restricted sense as indicative ofthe dual nature and functional independence of the cerebral hemispheres. On the basis of four individuals he studied, Magnan speculates that bilateral hallucinations may not be dependent upon peripheral lesions of the auditory apparatus, but rather upon the involvement of "the cortical sen-sorial centres". The term bilateral hallucination is used in opposition to the term * unilateral hallucination.

   References

   Blom, J.D., Sommer, I.E.C. (2009). Auditory hallucinations. Cognitive and Behavioral Neurology (in press).

   Lewis, W.B. (1885). Magnan on certain peculiar features in bilateral hallucinations. Brain,7, 562-564.