What happens when we stimulate a brain in local regions? Some possibilities:

  1. We may trigger an action without the subject's awareness of the action;
  2. We can trigger an action in a subject, but we cannot trigger a subject's will to perform this action;
  3. We can't trigger an action without awareness of subject;
  4. We cannot trigger an action without awareness of subject to his own action;

What are the results??

What I felt is 2, 4 are correct options because when some BMI devices are used subject is forcefully made to make a move. Here we are not changing his will to move but he is aware that he is moving.

  • 3
    $\begingroup$ I think without specification of the brain area, and/or specification of the mental process, and/or specification of the type/strength of the stimulus that the question is too broad. E.g., above-threshold stimulation of the motor cortex with TMS results in muscle twitches that are seen and felt by the subject & above-threshold stim. of V1 results in perceivable phosphenes. However, just-above-threshold stimuli in both cases may cause motor/visual activity so small that without focusing on the effect it may go unnoticed, especially against a background of spontaneous physiological activity. $\endgroup$
    – AliceD
    Jun 16 '15 at 0:13
  • 2
    $\begingroup$ @AliceD - I think your comment gives a nice 'it depends' kind of answer that would be appropriate. $\endgroup$ Jun 16 '15 at 12:42
  • 1
    $\begingroup$ What is the difference between 3 and 4? They read the same to me. $\endgroup$
    – Krysta
    Jun 16 '15 at 12:45

You should check out the article on Wikipedia: https://en.wikipedia.org/wiki/Neuroscience_of_free_will#Other_related_phenomena

Though there is still some controversy surrounding some of the experiments, the overall evidence suggests that it's possible to trigger action without awareness, it's possible to manipulate the perception of intention (will) to action, and it's also possible to do both.

In one study, directly stimulating the pre-SMA caused volunteers to report a feeling of intention, and sufficient stimulation of that same area caused physical movement.[35] In a similar study, it was found that people with no visual awareness of their body can have their limbs be made to move without having any awareness of this movement, by stimulating premotor brain regions.[60] When their parietal cortices were stimulated, they reported an urge (intention) to move a specific limb (that they wanted to do so). Furthermore, stronger stimulation of the parietal cortex resulted in the illusion of having moved without having done so.


Short answer
It depends.

Because the answer to this question depends heavily on which brain region is stimulated, I will focus on the visual cortex. Electrodes implanted in the primary visual cortex (V1) can generate visual percepts (flashes of light, or phosphenes) in the blind. Specifically, cortical prosthetics placed on V1 can generate phosphenes in the blind, and have been successfully used to restore partial vision in the blind (Dobelle, 2000). The generation of phosphenes is then the 'action' you are referring to in your question.

However, it all depends on stimulation conditions whether phosphenes are actually generated; most notably the stimulus level (but also stimulus shape (waveform), stimulus duration etc.). Assuming there is above-threshold stimulation in the cortex, a noticeable phosphene will be evoked. So this would probably be categorized as option 2. The triggering of a subject's "will" is probably very difficult, as triggering a voluntary choice by external stimulation has not been done at this time, as far as I know.

In case of a just-above threshold V1 activation, a subject may see a phosphene on one stimulation, but not the next. Blind folks often have spontaneous activity in their visual system, which makes them see spontaneous random patterns of light, or even complex scenes (Ayton et al., 2015). In this case, a phosphene may be generated, but go unnoticed by the subject, which boils down to option 1 and proves option 3 and 4 to be untrue.

So on the basis of the example scenario of a visual prosthetic for the blind, options 1 and 2 are correct, dependent on whether the stimulus is far above threshold, or just above it. Options 3 and 4 are incorrect as they are incompatible with the first two options.

My answer can be translated to a (hypothetical) cortical implant on the motor cortex in, e.g., people suffering from paralysis or motor dysfunction due to, e.g., stroke or trauma. Also, transcranial stimulation of the motor cortex is a good example, where intense stimuli generate limb movements that are seen and felt by the subject, but near-threshold stimuli may evoke movements that may go unnoticed due to spontaneous muscle movements.

- Ayton et al. Ophthalmology (in press)
- Dobelle et al. ASAIO (2000), 46(1): 3-9


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.