From arousal to cognition: the integrative position of the prefrontal cortex

The neglected constituent of the basal forebrain corticopetal projection system: GABAergic projections

At least half of the basal forebrain neurons which project to the cortex are GABAergic. Whilst hypotheses about the attentional functions mediated by the cholinergic component of this corticopetal projection system have been substantiated in recent years, knowledge about the functional contributions of its GABAergic branch has remained extremely scarce. The possibility that basal forebrain GABAergic neurons that project to the cortex are selectively contacted by corticofugal projections suggests that the functions of the GABAergic branch can be conceptualized in terms of mediating executive aspects of cognitive performance, including the switching between multiple input sources and response rules. Such speculations gain preliminary support from the effects of excitotoxic lesions that preferentially, but not selectively, target the noncholinergic component of the basal forebrain corticopetal system, on performance in tasks involving demands on cognitive flexibility. Progress in understanding the cognitive functions of the basal forebrain system depends on evidence regarding its main noncholinergic components, and the generation of such evidence is contingent on the development of methods to manipulate and monitor selectively the activity of the GABAergic corticopetal projections.

Computational perspectives on dopamine function in prefrontal cortex

Dopamine and the prefrontal cortex are critical for thought and behaviour. Recently, computational models have tried to elucidate the specific and intricate roles of dopamine in the prefrontal cortex, at the neurophysiological, system and behavioral levels, with varying degrees of success.

Suicide, serotonin, and the brain

The involvement of impaired serotonergic functioning in the development of suicidal behavior is one of the best documented findings in biological psychiatry. It is, however, less clear in which way this dysfunction contributes to the occurrence of suicidal behavior. Correlational studies have demonstrated associations between peripheral measures of serotonergic function and characteristics such as impulsivity, disinhibition, anxiety, and/or behavioral inhibition. Postmortem and neuroimaging studies have provided insight in the localization of serotonergic dysfunction in the central nervous system. Nevertheless, results in this area of research have also been contradictory. Following a short overview of recent research findings on serotonin and suicidal behavior, this paper focuses on the involvement of the prefrontal cortex of the brain in the development of suicidal behavior and on the role of serotonin in its executive functions. Based on these considerations, suggestions for future research are discussed.