University Studies 15A: Consciousness I

University Studies 15A:Consciousness IHow can I get a helping hand?

I know I promised you a lecture on visual consciousness.But I realized I had one more crucial topic to discuss before we turn to the neuroscience of consciousness itself.That is:

When I raise my hand, how do I do it?Let me begin with a crucial point.If I pet my cat, if I am sad or happy, if I come here to lecture, I am indeed doing these things.Neuroscience can explain how I move my hand to pet my cat. It can and must explain this I, but it cannot explain this I away.I raise my hand.I raise my hand.I decide to raise my hand, and my hand raises.I decide to raise my hand, and my hand raises.What I want to talk about today are current neuroscientific accounts of the I in decision and action.Lets start with the easiest part, the action itself.

Primary Visual CortexVisual Association AreasAuditory CortexPrimary Somatosensory CortexSomatosensory Association AreasMotor CortexPremotor CortexPrefrontal CortexWe already know about the Motor Cortex and the Premotor Cortex.The Motor Cortex then sends activations to the cerebellum and spinal cord to actually move body parts.The functional connectivity is:

Note the reciprocal connections between the lateral prefrontal cortex and the Premotor cortexA major scholar of the PFC (Fuster) proposes that the brains system for muscle movement as output is organized like that for vision, in reverse.That is, the Primary Motor cortex, like V1 with its horizontal lines, structures the smallest elements of movement.The Premotor cortex is like the higher visual cortex: it assembles higher order aggregates of movementLPFC is like IT: it has patterns for learned complex movements, like raising an armSo, raising an arm, in one sense may be very simple: just activate the right assembly of neurons in the LPFC and up it goes.The problem then is how do I decide to activate the assembly of neurons in the LPFC to raise the arm.Before we turn to the I, let us look at the paired functions of decision and the execution of decisions.

System for Coordinating Goals and Actions

We have seen most of these regions before.The PPC (posterior parietal cortex) integrates activations from many, many sources and uses them to calculate saliency.The MTL (medial temporal lobe) is the system for episodic memory, which contributes to both goal calculation and attention calculation.

It should be stressed at this point that all memory has an affective valence, so that calculations of both goals and saliency directly use this information (plus current body information from the somatosensory cortex and the insula.)

The THAL (thalamus) appears to serve a gating function, but then it seems to serve a gating function in every system we have examined.The ACC (anterior cingulate cortex) is part of the saliency network closely connected to the insula. Its primary job seems to be to process complex states to resolve conflicts (i.e., calculate which of the many states eventually wins a Winner-takes-all activation battle). It uses memory activations to calculate the cost of actions, which it adds to the overall computation.The DLPFC (dorsolateral PFC) does the calculation of goals.How, then, does the PFC make decisions about goals?

Premotor PFCdl PFCvm PFCAmygHippocDAmotor BGcogn BGVentral strBehavioral gatingWM gatingMotivational gatingWM, goalsif-then scenariosFast learningArbitrary associationsOrbitofrontal Cortex

That is, the VMPFC and VLPFC also have their say in calculation of goals by contributing calculations based on the value (valence) of the objects.I have added the Orbitofrontal Cortex, which we have talked about before, because it, like the VLPFC sums up values from information derived from the amygdala and the MTL memory system.Premotor PFCdl PFCvm PFCAmygHippocDAmotor BGcogn BGVentral strBehavioral gatingWM gatingMotivational gatingWM, goalsif-then scenariosFast learningArbitrary associationsOrbitofrontal Cortex

The diagram also shows that the basal ganglia also serve a variety of gating functions (increasing or decreasing the influence of particular activation connections) based on their own activation state (which in turn are controlled by both top-down (memory) and bottom-up (sensory) connections)Taken together, we see the processes of decision derive from various sets of calculations based on values assigned to current sensory states and to patterns in high-order memory. The calculations are negotiated in the lateral PFC cortex and the result, lift arm is activated in the cortical motor system.Premotor PFCdl PFCvm PFCAmygHippocDAmotor BGcogn BGVentral strBehavioral gatingWM gatingMotivational gatingWM, goalsif-then scenariosFast learningArbitrary associationsOrbitofrontal CortexNow we can deal with the I.At a very simple level (and neuroscientists like to start with simple levels), a sense of agency arises because I decide to lift my arm, and my arm lifts, therefore I lifted my arm.That is, the brain confirms the relationship between the executive activation and the perceived sensory/interoceptive result:

Of course, once you have a model, you can fiddle with it:For example, experimenters had subjects (with their heads in MRI imaging machines) put on gloves that tracked the motion of fingers and then have the subjects watch their hands on a computer display and have them move their fingers.The experimenter can then vary the degree of correspondence between the movements of the displayed hand and the subjects actual movement.Unexpected results make the parts of the brain involved in intentional binding very active:

Drawing on this sort of work, neuroscientists are beginning to examine such questions as the neural correlates of free will.Again, they start with simple models: if subjects are instructed either to follow a set instruction when they see a cue or allowed to freely choose their response (within a constrained set of choices), what additional regions become active in the free choice scenario?What they discover is that the brains response is in an area (the right inferior parietal cortex) that is part of a pattern of connectivity and activation that is coming to be known as the intrinsic system, those connected brain regions that track internal states and are active whenever questions requiring self-reflection are asked.This intrinsic system in turn corresponds to the default mode network we already have discussed. The sense of converging models for how I arise as a coherent nexus in the neural systems of the brain has led one researcher to propose the following:

The Interoself system is the internal system that does the work of assigning valences and shaping episodic and semantic memory and assessing the on-going state of the bodyThe Exterosensorimotor system is the set of networks that handle input from and output to the world beyond the brainThe Integrative self system is what puts the two other layers together.In terms of brain regions, we have:

The author of the article (Todd Feinberg) defines the self as a unity of consciousness in perception and action that persists in time.Neuroscience does indeed suggest that there is an I in the system:Its just a bit complex.I can raise my hand, but much must work right and things can get in the way.Just ask Dr. Strangelove.