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A rather basic question, but I don't see answer in Google, so here it goes: Humans have thoughts, sometimes these thoughts carry with them motivations to act, urges, cravings, etc. All these can make a person start moving to accomplish something.

For example: "I'm rather bored, I think I will go get a snack". What happens the moment I cross the threshold from thinking to actually getting up to get a snack?

What happens the moment the person starts to act based on a thought? Where in the human brain does a thought trigger action?

Update: In response to an answer suggesting that in many cases action comes first and rationalization for action comes second:

The kind of action that I'm talking about comes after a longer period deliberation, where the current state is being weighted against the benefit of the action to take.

For example in the situations below, a person can deliberate for minutes:

  • A person is in bed and is very close to sleep, being comfortable and relaxed. Loud noises from the outside disturb the person's attempt to fall asleep. In this case the person can experience conflict between staying in bed (comfortable but disturbed) or going to find earplugs / shut the windows (uncomfortable, but potentially lessening the disturbance)
  • A person is trying to meditate, thus relaxing the body and unfocusing the mind. An itch on the foot is disturbing the meditation. Such person can either continue the current state while ignoring the discomfort or scratch the itch and potentially lose the meditative state.

In the examples above, two conflicting courses of action are evaluated by the brain. Due to the ongoing discomfort, it is possible to stay in this state of "almost making a decision" for quite some time. At a certain point the scale can tip into taking action to resolve the discomfort. What is it that causes the person to take action as opposed to inaction?

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    $\begingroup$ 'A rather basic question'. Not really. From a philosophical point of view and also from a cognitive-neuroscientific viewpoint there is a lot of discussion about whether or not thought causes action (although any neuroscientific markers of such a thing as thought are still missing, and noone really has a clue how the brain gives rise to phenomenological 'thought'). Probably all introductions to philosophy of mind give an overview of relevant lines of argument. I suggest reading such a book. I also suggest Alva Noë's 'Out of our heads' for an antibiologistic approach to consciousness. $\endgroup$ – bunsenbaer Aug 25 '15 at 17:59
  • $\begingroup$ @AlexStone, the 3 examples you have now all seem to be related to some kind of "balance". Like if I'm working, and I feel the need to go to the bathroom, then I may not go right away, and wait until the urge to go to the bathroom exceeds the urge to continue working (ie, until the "balance" is tipped). Is that what you are asking about? Or are you trying to find examples of deliberation preceding action, as in solving a complex math problem? The former case doesn't seem as though thought plays a role in the decision, so that's why I'm still confused. $\endgroup$ – Arnon Weinberg Aug 26 '15 at 21:06
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There are many areas of the brain that are associated with planning complex behavior. This is because planning and executing are mediated by the brain's capacity for executive functioning, and EF is further associated with many areas of the brain -- in this case, the the frontal lobes, the prefrontal cortex, the caudate nucleus, and the putamen all seem to play a role.

What typically happens is that a thought is formed ('I'm hungry, I want a cookie', etc.), and then potential actions are envisioned and evaluated for their predicted effect, in line with the common coding theory of the relationship between perception and action. From a functional standpoint, the caudate nucleus selects the appropriate action based on an evaluation of the outcome of the action. [1] [2]

The more complex the task, the more cognitive strategies you may need to use, and these are mediated by your executive functioning ability. Cognitive shifting or task switching, information updating and monitoring ("updating"), and inhibition (or the 'tuning out' of irrelevant stimuli) all play a role in planning and executing complex tasks, or sequences of behavior. [3] For example, the ability to act in momentarily unpleasant yet beneficial ways (i.e. going to the gym) requires cognitive inhibition of more immediately gratifying, yet irrelevant stimuli (i.e. sitting on the couch, eating pleasurable food). For tasks of this nature, the frontal lobe plays a greater role.

Certain neurotransmitters also play a role in your ability to stay focused and dedicated to a task. Dopamine in particular is responsible for motivation (including the motivation to act), and norepinephrine is responsible for vigilance of attention, thus increasing the likelihood that an action will be performed and completed successfully. With a reduction in these neurotransmitters, you may demonstrate attentional shifts. Long-term, uncontrollable shifts in attention are often representative of an underlying disorder, such as attention-deficit disorder.


Sources used:

[1] Grahn, Jessica; John A. Parkinson; Adrian M. Owen (12 April 2009). "The role of the basal ganglia in learning and memory: Neuropsychological studies". Behavioral Brain Research 199 (1): 53–60.

[2] Oury Monchi, Michael Petrides, Antonio P. Strafella, Keith J. Worsley, Julien Doyon (Feb. 2006). Functional role of the basal ganglia in the planning and execution of actions. Ann Neurol. 59(2): 257–264.

[3] Miyake A1, Friedman NP, Emerson MJ, Witzki AH, Howerter A, Wager TD. (Aug. 2000) The unity and diversity of executive functions and their contributions to complex "Frontal Lobe" tasks: a latent variable analysis. Cogn Psychol. 41(1):49-100.

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  • $\begingroup$ Good, concise take on the cognitive angle (+1), except the last paragraph where it spontaneously drifts into nonsense. "With an abundance of these neurotransmitters, you can see a task through to completion"? Yes, I suppose in some sense, but in another sense, depending on where that abundance happens to be and when it happens to be there, you might also see the 9th dimension. $\endgroup$ – Christian Hummeluhr Aug 24 '15 at 20:30
  • $\begingroup$ @ChristianHummeluhr Agreed, I phrased that sentence terribly. Thanks for catching that. I'll edit it in a short moment. $\endgroup$ – Sydney Maples Aug 24 '15 at 20:39
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    $\begingroup$ It's not the sentence. Neurotransmitters do different things depending on when and where they're released. Point being: talking about neurotransmitters being "for" this or that in general doesn't make sense. $\endgroup$ – Christian Hummeluhr Aug 25 '15 at 8:32
  • $\begingroup$ @ChristianHummeluhr That is very true, but the same could be said about anything in this post, e.g. my assertion that the caudate nucleus selects the appropriate action. The caudate does many different things depending on the circumstance, but for the purposes of the question, only the action selection is relevant. In the case of dopamine/NE, their relevance to the question is in their reward/attentional aspects. I don't think its unfair to say that they are most 'responsible' for motivation/attention respectively, because they are most responsible. $\endgroup$ – Sydney Maples Aug 25 '15 at 16:00
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    $\begingroup$ No one should be talking about locations being "for" anything, either. Nonsense. $\endgroup$ – Christian Hummeluhr Aug 26 '15 at 6:54
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All actions a person might take are ultimately a matter of using one's muscles. So in that sense, your question --

What happens the moment the person starts to act based on a thought? Where in the human brain does a thought trigger action?

--probably ought to point us most to the motor cortex, since this area in the brain is most directly responsible for planning and "commanding" the patterns of activity of the muscles of the body as part of thought-driven (that, is conscious and willed) actions, though by use of neurons in subordinate areas of the nervous system, like the brain stem or the spinal cord, which then directly stimulate the target muscles to contract so as to produce the action.

So, just prior to actually moving as part of the conscious action (speaking, moving one's arm, etc.), there will be a change of activity of the neurons of the motor cortex that is ultimately responsible for those movements.

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