Temporal lobe lesions that leave hearing intact may cause a hearing disorder in which sounds are perceived as being louder or less loud than normal. Sounds or words may seem strange or disagreeable, or they may seem to be repeated, a kind of sensory perseveration. If auditory hallucinations are also present, they may undergo similar alterations. Such paracusias may last indefinitely and, by changing timbre or tonality, alter musical appreciation as well.
With lesions of the temporal lobes, these may be elementary (murmurs, blowing, sound of running water or motors, whistles, clangs, sirens) or complex (musical themes, choruses, voices). Usually sounds and musical themes are heard more clearly than voices. Patients may recognize hallucinations for what they are, or they may be convinced that the voices are real and respond to them with intense emotion. Hearing may fade before or during the hallucination.
In temporal lobe epilepsy, the auditory hallucinations are known to occur alone or in combination with visual or gustatory hallucinations, visual distortions, dizziness, and aphasia. There may be hallucinations based on remembered experiences (experiential hallucinations, in the terminology of Penfield and Rasmussen).
The anatomy of lesions underlying auditory illusions and hallucinations, formerly the province of study by ablative lesions, is currently being studied using functional imaging techniques. In some instances, these sensory phenomena have been combined with auditory verbal (or nonverbal) agnosia; the superior and posterior parts of the dominant or both temporal lobes were then involved. Clinicoanatomic correlation is difficult in cases associated with tumors that distort the brain without completely destroying it and that also cause edema of the surrounding tissue. Moreover, it is often uncertain whether symptoms have been produced by destruction of tissue or by excitation, that is, by way of seizure discharges. Elementary hallucinations have been reported with lesions of either temporal lobe, whereas the more complex auditory hallucinations and particularly polymodal ones (visual plus auditory) occur more often with left-sided lesions. It should also be noted that complex but unformed auditory hallucinations (e.g., the sound of an orchestra tuning up), as well as entire strains of music and singing, also occur, inexplicably, with lesions that appear to be restricted to the pons (pontine auditory hallucinosis, as noted in Chap. 14).
It is tempting to relate complex auditory hallucinations to disorders in the auditory association areas surrounding the Heschl gyri, but the available data do not clearly justify such an assumption. In schizophrenic patients, the areas activated during a period of active auditory hallucinosis include not only Heschl gyri but also the hippocampus and other widely distributed structures mainly in the dominant hemisphere (see Chap. 49).
In the superior and posterior part of the temporal lobe (posterior to the primary auditory cortex), there is an area that responds to vestibular stimulation by establishing one’s sense of verticality in relation to the environment. If this area is destroyed on one side, the only clinical effect may be a transient illusion that the environment is tipped on its side or is upside down; more often, there is only subtle change in eye movements on optokinetic stimulation. Epileptic activation of this area induces vertigo or a sense of disequilibrium. As pointed out in Chap. 14, pure vertiginous epilepsy does occur but is a rarity, and if vertigo precedes a seizure, it is usually momentary and quickly submerged in other components of the seizure.