Context-dependent reasoning in a cognitive bias task Part II. SPECT activation study.

A cognitive bias task (CBT) delineates two different cognitive selection mechanisms in the prefrontal cortex. To identify functional anatomy of context-dependent reasoning, we used technetium-99mhexamethyl- propyleneamine oxime (99mTc HM-PAO) single photon emission computed tomography (SPECT) and statistical parametric mapping. Twelve right-handed men 20-24 years old were instructed to look at a target card and then select the choice card (among two) that they preferred (modified CBT; mCBT). They also selected a choice card 2 weeks later without prior presentation of a target card (control task). In both tasks, 99mTc HM-PAO was injected intravenously about 15 s after initiation of the mCBT or control task. Brain images were obtained using a gamma camera and reconstructed by a UNIX-based workstation. Statistical analysis compared all activated images to control images. Results associated with P values of less than 0.01 (Z score > 2.36) were depicted on T1-weighted magnetic resonance images. All subjects preferred choices more similar to the target. SPECT activation occurred bilaterally in the dorsolateral prefrontal cortices and middle temporal gyri during performance of the CBT. Additionally, the left inferior prefrontal cortex and left fusiform gyrus showed significant activation compared with the control task. A neural network linking the temporal and prefrontal cortices prominently seen in the left hemisphere participates in context-dependent reasoning. Knowledge of such neural systems is essential for understanding prefrontal lobe function and dysfunction.