Auditory processing deficits

Although chronic ketamine (repeated acute administration for 14 days) reportedly has no effect on the amplitude or latency of any ERP components, there does appear to be some lasting effects of chronic ketamine exposure (Maxwell et al., 2006b). In a study by Maxwell and colleagues, mice were treated with ketamine daily for 2 weeks, and then tested 1 week later. Ketamine decreased N40 amplitude, but not latency 7 days after last ketamine dose. These data indicate that chronic NMDA receptor hypofunction can lead to auditory processing deficits similar to those seen in schizophrenia patients (Maxwell et al., 2006b). 

Although auditory processing deficits have been associated with lead exposure in children (Perino and Emhart, 1974 Needleman et al, 1979), little evidence is available concerning the effects of lead exposure on hearing in children. Elevated hearing thresholds have been observed in several studies of lead workers (reviewed by Repko and Corum, 1979), but no systematic audiometric evaluations of lead-exposed children have been reported until recently. 

There is hot a great deal of consistency in the areas of functioning where deficits are reported. Needlen an ei al (1979) reported deficits in verbal performance and auditory processing, but these have not been found by other workers who have assessed the same area, and in the case of the Seashore Rhythm test, used the same test (Smith ei al, 1983 Hansen ei al, 1985). 

Umbricht D, Schmid L, Roller R, Vollenweider FX, Hell D, et al. 2000. Ketamine-induced deficits in auditory and visual context-dependent processing in healthy volunteers Implications for models of cognitive deficits in schizophrenia. Arch Gen Psychiatry 57 1139-1147. 

Javitt DC, Shelley AM, Silipo G, Lieberman JA. 2000. Deficits in auditory and visual context-dependent processing in schizophrenia Defining the pattern. Arch Gen Psychiatry... 

As well as hallucinations and delusions, schizophrenia is characterized by deficits in information processing. Schizophrenics have difficulty suppressing irrelevant environmental stimuli. This is referred to as sensory gating or prepulse inhibition, and commonly measured with auditory evoked potentials. When two stimuli, such as sounds, are presented within 30-500 msec, the response to the second stimulus rapidly decreases upon repeated presentations in healthy people, but not in persons with schizophrenia (Braff et al., 2001). This deficit is found in family members of patients with schizophrenia, and has been linked to the alpha-7 nicotinic receptor gene. The deficit is reversed by nicotine on an acute basis, and by some antipsychotic drugs. Alpha-7 nicotinic agonists are under development as treatment for schizophrenia (Martin et al., 2004). 

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