Unconscious determinants of free decisions in the human brain

by Chun Siong Soon Marcel Brass Hans-Jochen Heinze & John-Dylan Haynes

Last Annotated: 10/13/15

Full article: http://www.rifters.com/real/articles/NatureNeuroScience_Soon_et_al.pdf

the outcome of a decision can be encoded in brain activity of prefrontal and parietal cortex up to 10 s before it enters awareness. This delay presumably reflects the operation of a network of high-level control areas that begin to prepare an upcoming decision long before it enters awareness.

it has been suggested that this subjective experience of freedom is no more than an illusion and that our actions are initiated by unconscious mental processes long before we become aware of our intention to act. In a previous experiment, electrical brain activity was recorded while subjects were asked to press a button as soon as they felt the urge to do so. Notably, their conscious decision to press the button was preceded by a few hundred milliseconds by a negative brain potential, the so-called ‘readiness potential’ that originates from the supplementary motor area (SMA), a brain region involved in motor preparation.

Here we directly investigated which regions of the brain predetermine conscious intentions and the time at which they start shaping a motor decision. Subjects who gave informed written consent carried out a freely paced motor-decision task while their brain activity was measured using functional magnetic resonance imaging (fMRI;

****  most of the intentions (88.6%) were reported to be consciously formed in 1,000ms before the movement

As expected, two brain regions encoded the outcome of the subject’s motor decision during the execution phase: primary motor cortex and SMA (Fig. 2).Next, we addressed the key question of this study, whether any brain region encoded the subject’s motor decision ahead of time. Indeed, we found that two brain regions encoded with high accuracy whether the subject was about to choose the left or right response prior to the conscious decision

********** (note: pre-conscious decisions) The first region was in frontopolar cortex, BA10. The predictive information in the fMRI signals from this brain region was already present 7 s before the subject’s motor decision. Taking into account the sluggishness of BOLD responses, the predictive neural information will have preceded the conscious motor decision by up to 10 s.

There was a second predictive region located in parietal cortex stretching from the precuneus into posterior cingulate cortex. Notably, there was no overall signal increase

the predictive information was encoded in the local spatial pattern of fMRI responses, which is presumably why it has not been noticed before.

****  Finally, we also assessed the degree to which the timing of the decision could be predicted ahead of time. We found that decoding of the time decision was possible as early as 5 s preceding the motor decision, but mainly from pre-SMA and SMA

Thus, there appears to be a double dissociation in the very early stages between brain regions shaping the specific outcome of the motor decision and brain regions determining the timing of a motor decision. At later stages, right before the conscious decision, both of these regions begin to encode timing and handedness information

****  Taken together, two specific regions in the frontal and parietal cortex of the human brain had considerable information that predicted the outcome of a motor decision the subject had not yet consciously made. This suggests that when the subject’s decision reached awareness it had been influenced by unconscious brain activity for up to 10 s, which also provides a potential cortical origin for unconscious changes in skin conductance preceding risky decisions.

This preparatory time period in highlevel control regions is considerably longer than that reported previously for motor-related brain regions1, and is considerably longer than the predictive time shown by the SMA in the current study (Supplementary Fig. 5). Also, in contrast with most previous studies, the preparatory time period reveals that this prior activity is not an unspecific preparation of a response. Instead, it specifically encodes how a subject is going to decide.

Notably, the lead times are too long to be explained by any timing inaccuracies in reporting the onset of awareness, which was a major criticism of previous studies. The temporal ordering of information suggests a tentative causal model of information flow, where the earliest unconscious precursors of the motor decision originated in frontopolar cortex, from where they influenced the buildup of decision-related information in the precuneus and later in SMA, where it remained unconscious for up to a few seconds.