We have reported a blood flow increase in the prefrontal cortex during the performance of the computer version TMT. Although TMT-A was first performed and followed by TMT-B in the previous study, the order was reversed in the present study,i.e., TMT-B was first performed and then followed by TMT-A, and differences in the change of blood flow were compared between the two modes of TMT.

Nine healthy student volunteers (20.7 ± 1.6 yr) performed two different sets of TMT-B. After a resting period of 30 sec, they performed four different sets of TMT-A. Changes of oxyHb and deoxyHb were monitored by 22-channel NIRS from 30 sec before the start of TMT-B through 30 sec after the end of TMT-A. The mean changes of blood flow over a period of 10 sec just before the start of TMT-B and TMT-A, and over a period of 100 sec after the start of TMT-B and TMT-A were determined.

The increase of oxyHb was prominent in the right lateral prefrontal cortex.

The results suggest that the blood flow increases in the prefrontal cortex during the start of either TMT-A or TMT-B. The location of blood flow increase did not change whether TMT-B was performed first or after TMT-A. Therefore, the blood flow increase observed only in the right prefrontal cortex in the previous study could not be due to familiarization of the test. In contrast, TMT-A apparently exhibits a familiarization effect, since blood flow increase was not observed when TMT-A was performed after TMT-B.