Predicting free choices for abstract intentions

Abstract

Unconscious neural activity has been repeatedly shown to precede and potentially even influence subsequent free decisions. However, to date, such findings have been mostly restricted to simple motor choices, and despite considerable debate, there is no evidence that the outcome of more complex free decisions can be predicted from prior brain signals. Here, we show that the outcome of a free decision to either add or subtract numbers can already be decoded from neural activity in medial prefrontal and parietal cortex 4 s before the participant reports they are consciously making their choice. These choice-predictive signals co-occurred with the so-called default mode brain activity pattern that was still dominant at the time when the choice-predictive signals occurred. Our results suggest that unconscious preparation of free choices is not restricted to motor preparation. Instead, decisions at multiple scales of abstraction evolve from the dynamics of preceding brain activity.

Fig. 1.

Measuring the onset and content of spontaneous abstract intentions. A trial began with a continuous series of stimulus frames refreshed every second, each consisting of a central fixation point, a letter below it, a single-digit number above it, and four single-digit response options, one in each corner. Immediately when participants felt the spontaneous urge to perform either adding or subtracting, they first noted the letter on the screen (frame 0 relative to time of decision). The chosen arithmetic task was then performed on the numbers presented above the central fixation in the next two stimulus frames (frames 1 and 2). The response options for the numbers in frames 1 and 2 were randomly presented in the four corners of the subsequent stimulus frame (frame 3): the correct addition answer, the correct subtraction answer, and two incorrect response options. Participants selected the correct answer for the chosen task by pressing one of four corresponding buttons, thereby revealing the content of their abstract decision. After the response was given, four letter options were presented from which participants selected the letter presented at frame 0, thereby revealing the time of conscious decision.

Fig. 2.

Decoding the outcome of abstract decisions before and after they reach conscious awareness. Projected onto the medial cortical surface are brain regions that predicted the outcome (red) of the abstract decision before it was consciously made (MNI coordinates). Inset shows similar results for the decoding of free motor decisions before conscious awareness in our previous study (2). The lateral surface shows the region that encoded the outcome of the decision after it became conscious. Line graphs depict for each cortical region the accuracy with which the abstract decision to perform addition or subtraction could be decoded at each time (error bars, SE; chance level, 50%). The vertical red line indicates the point of conscious decision, and the vertical gray dashed line indicates the onset of the next trial. Given the hemodynamic delay, information available at 0 s would have been a result of neural activity occurring a few seconds earlier. Please note that none of the points below chance level was statistically significant and should thus be attributed to random fluctuation.

Fig. 3.

Changes in overall default mode network activity for spontaneous motor and abstract intentions. (A) For both motor (Left) and abstract (Right) tasks, the DMN (blue; P < 0.0001) and choice-predictive (red; P < 0.0001) regions are projected onto the medial cortical surface, with overlapping voxels rendered in green. Please note that volume rendering projects regions from different depths onto the medial plane. (B) Activation time courses of the DMN (black line, left axis) are plotted together with the classification accuracies for precuneus/posterior cingulate (green dotted line, right axis) and frontopolar cortex (cyan dotted line, right axis). For both motor (Left) and abstract (Right) tasks, the default mode activity and the predictive information peaked roughly around the same time before conscious decision. The DMN during this early preparatory phase still resembled typical off-task or “resting” period activity, whereas parietal and prefrontal signals already encoded the upcoming choice.