Russell D. Green

Expanding the response space in chronic schizophrenia: the relevance of left prefrontal cortex.

OBJECTIVE This study probed the ability of people with chronic schizophrenia to control their behavior in time by requiring them to deliberately vary responses within the temporal domain (i.e., to avoid regular inter-response intervals). METHODS Thirteen schizophrenia patients performed single finger movements (at moments of their own choosing) in an event-related functional magnetic resonance imaging paradigm. Their performance was computed using the coefficient of variation of inter-response interval duration. RESULTS Task performance was positively correlated with activation of left lateral prefrontal cortex. Post hoc analyses revealed an inverse correlation between activation in this region and severity of attentional impairment. CONCLUSION These findings implicate left lateral prefrontal cortex in the modulation of the temporal response space in schizophrenia and imply greater attentional (executive) impairment among those who fail to modulate their behavior in time.

Toward a Cognitive Neurobiological Account of Free Association

Free association has been central to psychoanalytic theory and practice for over a century, yet its physiology has largely been ignored. When viewed from a cognitive neurobiological perspective, the process resembles a minimally constrained executive task, one that might engage the left dorsolateral prefrontal cortex. To test this hypothesis, we used functional magnetic resonance imaging to detect neural activity while subjects performed overt, vocal free association in the scanner. Twelve healthy subjects performed three active tasks—vocal free association, orthographic (letter) fluency, and semantic (category) fluency—alternating with a baseline condition, word repetition. Stimulus administration and overt response performance occurred during periods of scanner silence. Each subject was scanned three times, the order of conditions counterbalanced across scans. Statistical parametric mapping was used to perform a mixed-effects analysis of those images acquired. We found that, in common with both verbal fluency tasks, free association was accompanied by activation of the left dorsolateral prefrontal cortex. Indeed, it elicited significantly greater activation in adjacent areas. The main effect of “task,” common to all three active conditions, revealed an extensive network of activation within executive brain regions (including bilateral dorsolateral prefrontal and anterior cingulate cortices). While free association has been considered a probe of the “unconscious,” these data suggest that, early on in the process, under experiment conditions, this behavior engages components of the prefrontal executive (specifically, on the left). This finding points to a possible congruence between psychological accounts of “ego” function and neuropsychological accounts of a cognitive executive instantiated in prefrontal systems.