Hemodynamic and electrophysiological study of the role of the anterior cingulate in target-related processing and selection for action.

A number of experiments requiring attention or other complex cognitive functions have found substantial activation in the anterior cingulate cortex (ACC). Some of these studies have suggested that this area may be involved in "selection for action," such as for selecting to respond to a target stimulus. Here, positron emission tomography (PET) and event-related potentials (ERPs) were used to study the effects of target probability during a demanding visual spatial attention task, in which the target percentage was either low (2%, 1 per approximately 26 sec) or high (16%, 1 per approximately 3.5 sec). As expected, ERPs to detected targets evoked large, bilaterally distributed P300 waves. The PET showed strong activation of the ACC, particularly dorsally, during all the attend conditions relative to passive. However, these PET activations did not significantly differ between the few-target and many-target conditions, showing only a small trend to be larger in the many-target case. Such results indicate that the bulk of the ACC activation does not reflect selection for action per se, while also suggesting that the ACC is not a likely source of the P300 effect. The current data, however, do not argue against the ACC serving a role in maintaining a vigilant or anticipatory state in which one may need to select for action, or in continually or repeatedly (i.e., for each stimulus) needing to resolve whether to select to act or to not act.