Schizophrenia is associated with deficits in using context to establish
prepotent responses in complex paradigms and failures to inhibit prepotent
responses once established.
To assess prepotent response establishment and inhibition in patients
with schizophrenia using event-related brain potential (ERP) and functional
magnetic resonance imaging (fMRI) in a simple NoGo task. To combine fMRI and
ERP data to focus on fMRI activations associated with the brief (approximately
200 ms) moment of context updating reflected in the NoGo P300 ERP component.
Design and Setting
We collected ERP and fMRI data while subjects performed a NoGo task
requiring a speedy button press to X stimuli (P =
.88) but not to K stimuli (P = .12). The ERPs were
collected at the Veterans Affairs Palo Alto Health Care System, Palo Alto,
Calif; fMRIs were collected at Stanford University, Stanford, Calif.
We recruited patients with DSM-IV schizophrenia
(n = 11) from the community and the VA hospital and sex- and age-matched healthy
control subjects (n = 11) from the community.
Main Outcome Measures
Behavioral accuracy, P300 amplitudes and latencies, and fMRI activations
suggested that patients with schizophrenia did not establish as strong a prepotent
tendency to respond to the Go stimulus as healthy subjects. In healthy subjects,
NoGo P300 was related to activations in the anterior cingulate cortex, dorsal
lateral prefrontal cortex, and right inferior parietal lobule and caudate
nucleus, perhaps reflecting conflict experienced when withholding a response,
control needed to inhibit a response, and stopping a response in action, respectively.
In patients with schizophrenia, NoGo P300 was modestly related to activations
in the anterior cingulate cortex, which is consistent with experiencing conflict.
The difference in ERP and fMRI responses to Go and NoGo stimuli suggested
that inhibiting a response was easier for patients with schizophrenia than
for healthy subjects. Correlations of P300 and fMRI data suggested that patients
with schizophrenia and healthy subjects used different neural structures to
inhibit responses, with healthy subjects using a more complex system.