Prefrontal Contributions to Delayed Spatial and Object Alternation: A Positron Emission Tomography Study

Delayed alternation tasks are frequently used as probes of frontal lobe functioning. To clarify the neural substrates of delayed alternation performance in humans, the authors measured 15 regional cerebral blood flow with H2 O positron emission tomography in healthy subjects as they performed delayed spatial and object alternation. Consistent with the monkey lesion literature, increased dorsolateral prefrontal activity emerged during delayed spatial alternation but not delayed object alternation, whereas orbitofrontal activations emerged in both alternation tasks. The possible cognitive processes contributing to the orbitofrontal and dorsolateral prefrontal involvement in delayed alternation are discussed. Additional activations localized to several nonfrontal regions suggest caution in interpreting alternation deficits in patients as strictly reflecting frontal lobe impairment. Delayed alternation tasks have been widely used as probes of frontal lobe functions in both humans and animals. These tasks require subjects to select one of two objects on each trial, with the correct response correspondin

Brain activity in ventromedial prefrontal cortex correlates with individual differences in negative affect

Individuals differ in the extent to which they experience negative mood states over time. To explore the relationship between individual differences in negative affect (NA) and brain activity, we asked healthy subjects participating in positron-emission tomography scans to rate the extent to which they had experienced NA terms during the month before scanning. In two independent samples of subjects, resting regional cerebral blood flow within the ventromedial prefrontal cortex (VMPFC) correlated with ratings of NA. The finding converges with recent evidence implicating the VMPFC in emotional and autonomic processing. Moreover, it demonstrates that variability in basal VMPFC activity across subjects is related to individual differences in subjective emotional experience