Re: How does THC affect the brain in relation to perception and focus?

Hi Mike,

     Interesting question(s). I'll address your main question concerning effects of THC first, and then the one about patterns of neuron activity.

     I think your first question is: "How does THC seem to increases focus or lucidity?" I'll first describe a bit background on the cannabinoid system in the brain, and then address what I found re: attention/focus. I got most of my info from an article entitled "Cannabinoid modulation of executive function" by Pattij, et al, in the European Journal of Neuroscience (585, pp 458-463, 2008).
     As you may know, THC binds to specific receptors in the brain. Normally, they are bound by 'intrinsic' cannabinoids or 'endocannibinoids' - neuronally released substances which activate those receptors. But the location of these receptors is as important as their mere presence. They appear to be localized to synapses which release norepinephrine, dopamine, serotonin, and acetylcholine (among other synapse types). These are neurotransmitters that are associated with affect and attention. So cannabinoid receptors are in the right place to modulate these 'higher cognitive' brain functions.

     But what I just described is at the level of neuron biology, and not behavior. People have tested various endocannabinoid receptor activators and blockers in rats and mice. Two interesting parameters are mentioned in the review I cite. One has to do with attention: in rats, they tested animals for their ability to respond to a set of stimuli, and they find the animals did more poorly after they were given a cannabinoid receptor activator. They conclude that attention is impaired by cannabinoids, but I'm not sure if they can rule out that the animal wasn't just focussed on something other than the task they were trying to get it to perform.
     The second parameter is termed 'behavioral flexibility,' which means the ability to switch your current mindset/attention/behavior to something else in the room. As you may guess, activation of cannabinoids makes animals less likely to switch their behavior in response to a new stimulus. One could argue that they are focussed on something so intently (like a song?), they will not be easily distracted (like I suggest at the end of the previous paragraph).
     However, as far as I know, we don't have a direct link between the data about a specific endocannabinoid function and the behavioral data. That is to say, I don't think anyone has shown that endocannabinoid receptors located on synapses that contain norepinephrine and acetylcholine are the ones responsible for the loss of behavioral flexibility, etc. So I can't provide a direct explanation for why focus is heightened after consuming THC, but I can say that the evidence so far is certainly consistent with your observations, and hints at potential mechanisms.

     Now to address your second question(s), which I believe is, "is it known what pattern of neuronal activity leads to perception, and could we activate it externally?" The short answer is no. We do know that highly organized patterns of activity are required for perception, and we even have observed neuronal activity en masse associated with the attending/perceiving brain (by functional MRI, or 'fMRI,' or by observing so called 'neuronal oscillations'). But we are far, FAR away from the ability to trigger those activity patterns in a controlled manner to induce perceptions (in a total recall/matrix kind of way).
     But an interesting nugget: people who are undergoing brain surgery (for epilepsy and cancer) are anesthetized locally on their scalps, but are awake. If a surgeon has to cut something out, s/he will want to test what part of the brain being cut! To do the tests, the surgeon electrically stimulates different parts of the patient's brain. Patients report smelling odors, recalling memories, and have 'deja vu' like feelings upon this stimulation. So the possibility of activating 'perceptions' is there. The problem is that they aren't likely to be in the exact same place for each person, and it's likely that people don't perceive identical stimuli in the same way. So it's unlikely that we can activate a specific set of feelings/perceptions in a meaningful way. So that's why I say the answer to your question is 'no.'

     I hope provides some helpful on what's known!
-Alex Goddard