MEG localization of cortex involved in attention processes during a driving task with conversation

Whole-head MEG imaging of 19 subjects was used to determine the neural mechanisms that modulate reaction times to visual events while watching a driving video, with and without a simulated cell phone conversation. The primary task was to watch the video and depress a foot pedal in response to a small red light presented to the left or below the driving scene at unpredictable times. The secondary task was a conversation. The subject pressed a button to answer a ring tone, and then covertly answered pre-recorded questions. The foot reaction times (RTs) were recorded. Conversation increased mean behavioral RT by 77 ms but did not affect the “miss” rate for the event lights. Partial Least-Squares and linear discriminant analysis of the MEG data extracted signals related to cortical processing underlying this RT effect. Linear regression analysis first identified MEG signals associated with RT. Locations of brain activity whose response correlated with RT were then imaged using the ICA-MR-FOCUSS technique. While performing the primary task without conversation, brain activity was found to be inversely related to RT in (1) right superior parietal lobe during the 200- to 300-ms interval after red light onset and (2) visual cortex during the 85- to 90-ms interval after red light onset. The magnitude of the change in cortical response with RT was substantially reduced by adding the conversation secondary task. Thus, conversation activated language-specific areas as expected, but also damped brain activity in the right superior parietal and visual regions. However, these laboratory findings should not be interpreted as if real-world conversations are driver distractions without on-road validation and comparison to the effects of other in-vehicle tasks.