Neuroimaging Studies

A small number of studies have used invasive techniques to study anterior cingulate function in humans, recording from or stimulating cingulate neurons during neurosurgery. Stimulation in ventral-rostral areas has been found to evoke autonomic changes in blood pressure and heart rate, visceromotor responses including salivation and vomiting, emotional responses including fear, agitation, and euphoria, and vocalizations with affective content. Anterior cingu-late stimulation has also been shown to evoke motor responses of the face, hands, and legs, evidence, perhaps, of areas in the human brain corresponding to the CMAs seen in nonhuman primate anterior cingulate cortex. Recordings in caudal regions have revealed neurons with activity that is modulated during attention-demanding tasks such as arithmetic and generating lists of words. Other neurons, in further caudal and inferior regions, show sensitivity to painful stimuli. Overall, the findings are consistent with those reported in the previous section. However, these invasive studies are necessarily infrequent, and their interpretation is complicated by the neuropsychologi-cal condition of the patients involved that necessitated the surgery. Therefore, the preceding findings notwithstanding, much of the current understanding of anterior cingulate function has stemmed from more noninvasive imaging methods that can be applied in neurologically intact subjects.

Most neuroimaging studies of anterior cingulate function have used positron emission tomography (PET) or functional magnetic resonance imaging (fMRI). Both techniques rely on a subtractive methodology, comparing activation in brain areas across different experimental conditions that are designed to isolate specific processes. Such comparisons reveal areas of activation—areas more activated in the experimental than in the control condition—and, less commonly, areas of deactivation. These methodologies have very good spatial resolution on the order of millimeters, but relatively poor temporal resolution on the order of seconds to minutes. Electrophysiological recordings, on the other hand, have poor spatial resolution, but excellent temporal resolution on the order of milliseconds. Findings based on either PET, fMRI, or electrophysiological recordings regarding the role of the anterior cingulate cortex in human behavior are described later by relative region. For the most part, rostral and ventral regions have been linked with affective behavior, and more dorsal and caudal regions have been linked to cognitively driven actions. A major debate regarding the function of this region has resided in the domain of cognition primarily.

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