Steady state responses: Electrophysiological assessment of sensory function in schizophrenia

Brenner, C. A., Krishnan, G., Vohs, J., Ahn, W.-Y., Hetrick, W. P., Morzorati, S., & O’Donnell, B. F. 2009. Schizophrenia Bulletin, 35(6), 1065-1077.


Persons with schizophrenia experience subjective sensory anomalies and objective deficits on assessment of sensory function. Such deficits could be produced by abnormal sig- naling in the sensory pathways and sensory cortex or later stage disturbances in cognitive processing of such inputs. Steady state responses (SSRs) provide a noninvasive method to test the integrity of sensory pathways and oscil- latory responses in schizophrenia with minimal task demands. SSRs are electrophysiological responses entrained to the frequency and phase of a periodic stimulus. Patients with schizophrenia exhibit pronounced auditory SSR deficits within the gamma frequency range (35–50 Hz) in response to click trains and amplitude-modulated tones. Visual SSR deficits are also observed, most promi- nently in the alpha and beta frequency ranges (7–30 Hz) in response to high-contrast, high-luminance stimuli. Visual SSR studies that have used the psychophysical properties of a stimulus to target specific visual pathways predomi- nantly report magnocellular-based deficits in those with schizophrenia. Disruption of both auditory and visual SSRs in schizophrenia are consistent with neuropatholog- ical and magnetic resonance imaging evidence of anatomic abnormalities affecting the auditory and visual cortices. Computational models suggest that auditory SSR abnor- malities at gamma frequencies could be secondary to g-aminobutyric acid–mediated or N-methyl-D-aspartic acid dysregulation. The pathophysiological process in schizophrenia encompasses sensory processing that proba- bly contributes to alterations in subsequent encoding and cognitive processing. The developmental evolution of these abnormalities remains to be characterized.