Neurophysiological Distinction between Schizophrenia and Schizoaffective Disorder

Abstract

Schizoaffective disorder (SA) is distinguished from schizophrenia (SZ) based on the presence of prominent mood symptoms over the illness course. Despite this clinical distinction, SA and SZ patients are often combined in research studies, in part because data supporting a distinct pathophysiological boundary between the disorders are lacking. Indeed, few studies have addressed whether neurobiological abnormalities associated with SZ, such as the widely replicated reduction and delay of the P300 event-related potential (ERP), are also present in SA. Scalp EEG was acquired from patients with DSM-IV SA (n = 15) or SZ (n = 22), as well as healthy controls (HC; n = 22) to assess the P300 elicited by infrequent target (15%) and task-irrelevant distractor (15%) stimuli in separate auditory and visual "oddball" tasks. P300 amplitude was reduced and delayed in SZ, relative to HC, consistent with prior studies. These SZ abnormalities did not interact with stimulus type (target vs. task-irrelevant distractor) or modality (auditory vs. visual). Across sensory modality and stimulus type, SA patients exhibited normal P300 amplitudes (significantly larger than SZ patients and indistinguishable from HC). However, P300 latency and reaction time were both equivalently delayed in SZ and SA patients, relative to HC. P300 differences between SA and SZ patients could not be accounted for by variation in symptom severity, socio-economic status, education, or illness duration. Although both groups show similar deficits in processing speed, SA patients do not exhibit the P300 amplitude deficits evident in SZ, consistent with an underlying pathophysiological boundary between these disorders.

Keywords: EEG; P300; event-related potential; schizoaffective disorder; schizophrenia.

Figure 1

Grand average ERPs (top row) and P300 scalp topography maps for Auditory and Visual Targets (far left and mid-left columns, respectively) and Auditory and Visual Task-Irrelevant Distractors (mid-right and far right columns, respectively) in healthy controls (HC; second row), patients with schizoaffective disorder (SA; third row) and patients with schizophrenia (SZ; fourth row). Latency windows capturing the P300 for each condition and group are indicated below each topographic map. The color-coding on the scalp topography maps reflects voltage for that group at that site. In the grand average plots, target ERPs are plotted from electrode Pz and task-irrelevant distractor ERPs are from Cz. ERPs are overlaid for HC (green tracings), SA (red tracings) and SZ (blue tracings) groups. Time is shown on the x-axis and voltage on the y-axis. Voltage scales are different for the different stimulus types. Positivity relative to the reference electrodes is plotted up.

Figure 2

Means for P300 amplitudes from Fz, Cz, and Pz are plotted for Auditory Targets (upper left), Auditory Task-Irrelevant Distractors (lower left), Visual Targets (upper right) and Visual Task-Irrelevant Distractors (lower right). Color-coding is the same as in Figure 1.

Figure 3

Scatterplots showing relationships between Illness Duration (years) and P300 amplitude elicited by Visual Task-Irrelevant Distractors (right) and Auditory Targets (left) for schizoaffective patients (red) and schizophrenia patients (blue).