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Although olfactory identification deficits in schizophrenia have been repeatedly demonstrated, some studies indicate that schizophrenia patients may also show an olfactory hypersensitivity. In addition, recent evidence points to impaired odor hedonics in schizophrenia. It was the aim of the present study to investigate olfactory information processing in schizophrenia patients with positive symptoms, by means of chemosensory event-related potential (CSERP) analysis. To control for modality-specific effects, these data were compared to visual event-related potentials (VERP), and in order to control for disorder-specific effects, the schizophrenia patients were compared to healthy controls as well as to patients with major depressive disorder (MDD). In each group, nine subjects were investigated. During EEG recording (32 scalp locations) two odors (positive valence: phenyl-ethylalcohol, negative valence: isobutyraldehyde) were presented using the constant flow method. Afterwards, two colors (red, yellow) were presented. The schizophrenia patients responded to both odors with shorter CSERP latencies than healthy controls and MDD-patients. This effect was most pronounced for the early processing (N1 component) of the emotionally negative odor. However, in response to colors, schizophrenia patients showed increased N1 latencies and a reduced P3 amplitude. It will be discussed whether schizophrenia patients with positive symptoms show a general processing advantage for emotionally negative (threat-related) information.

This paper addresses two questions related to the inherent association between breathing and odor perception: Does central nervous processing of odors change when an artificial breathing technique (velopharyngeal closure) is introduced and secondly, does odor processing vary with the oral breathing phase (inhalation or exhalation)? Chemosensory event-related potentials (CSERP) were obtained from eight female subjects while they were smelling an odor mixture (citral, eugenol, linalool, menthol and isoamylacetate). Each subject was required to perform spontaneous mouth breathing (120 trials) as well as the velopharyngeal closure technique (120 trials). Simultaneously, a thermistor monitored the phase of the respiratory cycle. The results reveal that the central nervous correlates of odor processing change with the breathing technique but not with the oral breathing cycle. The findings that early stimulus processing is faster (N1 latency) and late stimulus processing more pronounced (P3 amplitudes) when the subjects are breathing spontaneously are discussed with regard to attentional effects. The reduction of the N1 amplitude during the spontaneous breathing condition may be caused by larger latency variations and longer stimulus rise-times. Furthermore, it is concluded that the oral breathing cycle is less important than the nasal breathing cycle for olfactory information transmission.