[Abstract Title]. - Society for Neuroscience

Program#/Poster#: 288.16/RR23
Topic: F.01.f. Working memory
Support: Grant-in-Aid for Young Scientists (S) from the JSPS (19670001)
Title: Effective connectivity during task preparation reflects carry-over from a previous task
Authors: *R. AKAISHI, Y. MORISHIMA, V. RAJESWAREN, K. SAKAI;
Grad. Sch. of Med., Univ. of Tokyo, Tokyo, Japan
Abstract: We tend to repeat a same action knowing it is inappropriate in a new context. Task set
inertia, carry-over from a previous task, is thought to contribute to the tendency of perseveration,
such as slower and less accurate responses when we change from one task to another. Task set
inertia can not be eliminated even with a long preparation time for the next task. In the present
study we investigated the neural basis of task set inertia. Because task preparation was associated
with interregional connectivity, we hypothesized that task set inertia is also based on
interregional connectivity. In order to assess the connectivity at a specific timing during task
preparation, we used a combination of transcranial magnetic stimulation (TMS) and EEG. This
technique allows us to examine cortical effective connectivity, the efficiency of impulse
transmission from an activated area to other areas. We asked normal human subjects to perform
pro- or anti-saccade task based on a cue with a cue-target interval of 500 ms. We delivered a subthreshold
single-pulse TMS on the right frontal eye field (rFEF) at 400 ms after the cue. We
calculated the TMS evoked potentials by subtracting the EEG waveforms on no TMS trials from
those on TMS trials. On the TMS evoked potentials at 20-40 ms after the TMS, we conducted
two-way ANOVA with factors of previous and current task types. We found that the main effect
of previous task was significant but that of current task was not significant. We also found that
the TMS-evoked potential spread more broadly to posterior sites when saccadic responses were
slower on trials preceded by antisaccade tasks. These results might indicate that inhibitory
control required for antisaccade on a previous trial remains as effective connectivity. In contrast,
the ERP on trials without TMS at the corresponding time window exhibited significant main
effect of current task but non-significant effect of previous task. The time course of the ERP
during the whole preparation period confirmed the major effect of preparation for a current task.
Our results suggest that the control exerted during the execution of an antisaccade task on a
previous trial creates the effective connectivity, which, consistent with the properties of task set
inertia, persists during task preparation and modulates the task execution on the current trial. The
effective connectivity reflecting previous tasks might also underlie the perseveration in human
behavior.
Disclosures: R. Akaishi, None; Y. Morishima, None; V. Rajeswaren, None; K. Sakai, None.
Poster