Question:

Deliberation is the process of weighing alternative options. The aim of this study is to investigate neuronal correlates of a deliberation process resulting in a motor decision.

Methodology:

In this study, 23 young right-handed subjects (age: 18 - 27, 12 female) had to press a key with right or left hand depending on a visual Stroop stimulus. The Stroop stimulus consisted of a word indicating a colour written either in the corresponding colour (e.g. word “red” written in red / match condition) or written in a different colour (mismatch condition). Subjects had to deliberate to respond with the right hand in the match condition or with the left hand in the mismatch condition. High-density multi-channel EEG activity was recorded as well as behavioural data. In addition, reaction times of the deliberation tasks were compared with those of a corresponding simple motor task.

Results:

The reaction time in the deliberation task is significantly different from that observed during the simple motor task. Moreover, within the deliberation task the reaction times for the mismatch condition are significantly longer compared with those of the match condition. The EEG patterns observed in the primary motor cortex (Brodmann Area 4) during both tasks show clear differences. During the simple motor task, a typical pre-motor positivity is observed preceding the key press whereas during the deliberation task a strong negativity approximately 300 ms before movement onset is found. This negativity appears earlier in the left hemisphere than in the right one independent of the condition. Subtracting the motor task pattern from the EEG pattern of the deliberation task augments the preceding negativity, presumably attributing a required cognitive process.

Conclusions:

The deliberation process during movement decision is represented by an increasing negativity in the motor region before movement onset. As both hemispheres show a similar activation, it is assumed that competing motor plans are processed simultaneously. This result supports the idea for an involvement of the primary motor cortex in the deliberation process.

Supported by the Munich-Center for NeuroSciences - Brain and Mind (Nida-Rümelin 2011).