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Introduction
It is well established that the mechanical energy of sound waves which is amplified by the external and middle ears is transformed into electrical stimuli by the hair cells in the inner ear. This energy is transmitted by the ganglion cells and reaches the temporal lobe -through a number of ipsi and contralateral relays of excitatory and inhibitory stimuli - where functional neuronal groups interpret such impulses (Huxley 1928, Saunders 1997, Hudspeth 2000). However, there is paucity of information regarding the functional distribution and processing of these acoustic stimuli in the brain (Griffiths 2004) and there is no normal functional data base available. The question also arises if we are capable of storing this information in the form of auditory memory and if there is a cortical representation where this coded information is stored.
Having the sensation of listening to previous auditory perceptions, particularly of well known songs, has been previously described in patients with sensorineural hearing loss (Goycoolea 1994, Griffiths 2000, Tanriverdi 2001). It has also been reported in patients with inner ear disease in whom these musical perceptions have been precipitated by the administration of stimulant drugs or by the withdrawal of a sedative agent (Paquier 1992, Gilbert 1993, Gordon 1994). To our knowledge, to date, there are no definite studies available that would identify the cortical area involved in the generation of these musical perceptions.
In this study, single photon emission computerized tomography (SPECT) evaluation was conducted: A. Using auditory stimulation with pure tones in 4 volunteers with normal hearing. B. In a patient with bilateral profound hearing loss who had auditory perception of previous musical experiences, injected with Tc99m HMPAO while she was having the sensation of hearing a well known melody.
The purpose of this study is three fold:
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To determine which areas of the cerebral cortex are activated stimulating the left ear with pure tones, and what type of stimulation occurs (e.g. excitatory or inhibitory) in these different areas.
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To use this information as an initial step to develop a normal functional data base for future studies.
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To try to determine if there is a biological substrate to the process of recalling previous auditory perceptions and if possible, suggest a locus for auditory memory.
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