MEG-measured visually induced gamma-band oscillations in chronic schizophrenia: Evidence for impaired generation of rhythmic activity in ventral stream regions

Background: Gamma-band oscillations are prominently impaired in schizophrenia, but the
nature of the deficit and relationship to perceptual processes is unclear.
Methods: 16 patients with chronic schizophrenia (ScZ) and 16 age-matched healthy controls
completed a visual paradigm while magnetoencephalographic (MEG) data was recorded.
Participants had to detect randomly occurring stimulus acceleration while viewing a
concentric moving grating. MEG data were analyzed for spectral power (1-100 Hz) at sensorand
source-level to examine the brain regions involved in aberrant rhythmic activity, and for
contribution of differences in baseline activity towards the generation of low- and highfrequency
power.
Results: Our data show reduced gamma-band power at sensor level in schizophrenia patients
during stimulus processing while alpha-band and baseline spectrum were intact. Differences
in oscillatory activity correlated with reduced behavioral detection rates in the schizophrenia
group and higher scores on the “Cognitive Factor” of the Positive and Negative Syndrome
Scale. Source reconstruction revealed that extra-striate (fusiform/lingual gyrus), but not
striate (cuneus), visual cortices contributed towards the reduced activity observed at sensorlevel
in ScZ patients. Importantly, differences in stimulus-related activity were not due to
differences in baseline activity.
Conclusions: Our findings highlight that MEG-measured high-frequency oscillations during
visual processing can be robustly identified in ScZ. Our data further suggest impairments that
involve dysfunctions in ventral stream processing and a failure to increase gamma-band
activity in a task-context. Implications of these findings are discussed in the context of
current theories of cortical-subcortical circuit dysfunctions and perceptual processing in ScZ.