UN-conditioned reflex

(This is a joined postage and you might want to read the previous post before this one)

How long does it take between you wanting to move your arm, your brain getting ready to move your arm, and your arm actually moving? You probably never thought about it, because unless you’re a NERD, it doesn’t matter: it all falls under the definition of ‘automatic’. But NERD scientists value very small differences, as long as they are consistent, and some started to think about all these questions. We all know that voluntary movement start in the brain, but when?

Well, brave scientists went to measure. More precisely, they were to measure the ‘Anticipation Potential’ (AP) , which is a small change in the electrical current passing through the scalp before (1s or more) a rhythmic movement that is both involuntary (such as heartbeat) and voluntary (such as moving the arm. The measurement is taken by an electroencephalogram (EEG) , which is similar to an electrocardiogram, only it is done in the brain, with a bunch of electrodes glued to your head.

But the question they wanted to answer was another. They, the brave researchers, were on ‘urgency’, also called ‘preparation’ (W) , terms defined by the self-awareness of movement: that exact moment when you feel your arm… is going to move. Did you ever notice that? Well, like I said, it’s because everything happens so fast and we never stop to notice. But despite being a subjective event, its existence is very well characterized and documented. Stimulation of certain areas of the brain during open-head neurosurgery induces in patients an “involuntary and inexplicable desire to roll the tongue” or “move the arm”. The point is that the 1s between the change in the EEG and the movement of the arm seemed like a long time for a voluntary action and the researchers wanted to know if the urgency was even earlier.

For this, they devised the following experiment:

A group of volunteers sat comfortably, with electrodes on their heads and arms, looking at a wall where a circle, with rays similar to that of a clock, was drawn. Like I said, it looked like a watch, but it wasn’t. The spokes were in the same positions 12 positions, but one full turn of the pointer, actually a red laser dot, took only 2.56 s to complete the circumference.

The volunteers’ task was simple: they had to move freely, spontaneously, when they wanted their wrist and the fingers of their right hand (all volunteers were right-handed). When they made this movement, looking only at the clock in front of them, they had to keep (to report later – which makes all the difference in an experiment where variations occur in milliseconds) the position of the red light point at the exact moment when ‘ perceived’ the ‘preparation’. The ‘urgency’ of the movement.

Let’s face it, it was a great insight from the researchers (who were psychologists). The red light pointer was emitted by a computer, to which the EEG and the ‘electromyogram’ (EMG) were also connected , the sensor that measured the action potential of the skeletal muscle of the arm and that marked the ‘real’ beginning of the movement . With this, by reporting the position of the light pointer, such as noting the time marked on the clock for an event, researchers were able to transform a subjective experience into a computable measure. And so, the moment of ‘preparation’ (W) can be compared with the ‘anticipation potential’ (PR) , prior to the act, in the scalp and with the moment of voluntary contraction of the wrist, measured by the electromyogram (EMG) .

Open parentheses: different types of training and controls were carried out with the participants, to reduce bias and other types of interference, or artifacts, in the measurements or reports.

For example, 

“The movements were voluntary, with explicit instructions to be as spontaneous as possible (no planning). But also, they were external, induced by an observer touching the back of the person’s hand.” or “After 40 voluntary acts, the participants were asked about the existence of any movement that had not aroused the urgency (a type of surprise movement). These questions were asked to try to eliminate bias in participant reporting of events and increase confidence in the times that were actually reported.” Or “Two types of controls were employed. A report of the times of perception of performing the movement (M) and another of perceiving the stimulus in the hand to perform the movement (S)”.

 According to the authors, the participants were still easily able to differentiate between ‘urgency’ and any other type of planning perception or one that did not lead to a movement. Go figure…

Close parentheses.

The results were very clear: the PRs appeared around -500 ms before the action potentials measured by the EMG , which were taken as ‘zero time’ for the comparative measurements. So far so good: pulse movement (measured by EMG) was preceded by brain activity (measured by PR) by approximately 500 milliseconds.  Things got weird when they measured the ‘urgency’ (W) times  (the introspective and subjective perception of the decision to move the arm): they averaged –200ms (also in relation to the EMG)! That is: The decision to move the wrist was perceived 300 ms AFTER the brain started the process of moving the wrist!

The authors make several reservations: 

“The PR measured in the study, although good indicators, represent the activity of a small area, the supplementary motor region in the mesial neocortex” 

and other areas could be being activated for the ‘decision’ in another place of the brain. In fact,  an infinity of ‘initiation’ and ‘integration’ mechanisms of the signal in the brain, before it becomes conscious and becomes an action, could act in the brain. A ‘thought’ does not generate a potential difference sufficient to generate an EEG recording , and precisely for this reason it is so difficult to assess this subjective perception objectively. And this is also why the authors point out: 

“We can further speculate that there is an earlier phase of movement awareness that we are not able to recapitulate, or that cannot be stored in recent memory, given that the ability to report is linked to recent memory.“

But none of these caveats change the fact that the decision to move happens unconsciously. In the words of the authors:  

“We conclude that the initiation of a voluntary act in the brain, such as those studied here, can begin, and usually does, unconsciously“

Open parentheses: The term unconscious simply refers to all processes that are not expressed as a conscious experience. This may include, and is not distinguished from, preconsciousness, subconsciousness, and other unreportable unconsciousness processes. Close parentheses.

It is clear that the evidence for unconscious initiation of a voluntary act reported in this article applies to a very limited number of acts. However, a simple voluntary motor act such as the one reported here has always been considered an uncontroversial and ideal example of an engdogeneous and freely voluntary act.

“These considerations seem to limit individuals’ potential to exercise conscious control (such as initiating) over their actions. Considering that spontaneous voluntary acts can be initiated unconsciously, we could still imagine two conditions under which a conscious control could be exercised: a conscious ‘veto’ that ‘aborts’ the unconscious spontaneous process (which seems to find evidence even in the results of this experiment) and in processes where voluntary acts are neither spontaneous nor quick to respond.”

At best, scary. But at least now you have the perfect excuse for that sideways look when you pass a cute booty or a bolder neckline.

Published originally in 2012 in the “Voce que é biólogo…” blog in Portuguese

Libet B, Gleason CA, Wright EW, & Pearl DK (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act. Brain: a journal of neurology, 106 (Pt 3) , 623-42 PMID: 6640273