Effect of a cognitive task on online adjustments when avoiding stepping on an obstacle and stepping on a target during walking in young adults.

During locomotion, we respond to environmental and task changes by adjusting steps length and width. Different protocols involving stepping on targets and obstacle avoidance suggest the involvement of cortical and subcortical pathways in these online adjustments. The addition of a concomitant cognitive task (CT) can affect these online corrections depending on the neural pathway used. Thereby, we investigated the online adjustment using a target stepping task and a planar obstacle avoidance task in young adults and analyzed the effect of a CT on these adjustments. Twenty young adults executed two blocks of trials of walking performing the target task (TT) and obstacle avoidance task (OAT), with and without a concomitant CT. In the TT, participants stepped on a target projected on the ground, whereas in the OAT they avoided stepping on an obstacle projected on the ground. The target/obstacle could change its original position in four directions at contralateral foot contact on the ground. Overall, the CT did not affect the latency to start the adjustments due to target/obstacle change. The main changes were restricted to the frontal plane adjustments. The latency for the medial and lateral choices in the OAT was ~ 200 ms, whereas for the TT was ~ 150 ms. These results suggest the involvement of a slow cortical pathway in the OAT in the frontal plane modifications. In turn, the TT may be controlled by one of two fast adjustment neural pathways.