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