A Neural Theory of Mind

Paul Bush paul at phy.ucsf.edu
Thu Apr 25 18:36:15 EST 1996


Thanks very much for your post, very informative.

In article <4ll63r$5bv at eis.wfunet.wfu.edu>, laubach at biogfx.neuro.wfu.edu (Mark Laubach) writes:
|> I view an
|> activation of a spiny cell as indicating a coincident activation of a
|> collection of cortical cells distributed in different locations in
|> cortex and activations at different levels of the striatum  as
|> representing unique info occuring in relation to a common "event"
|> (e.g., a behavior, thought).

Great. Can I quote this sentence? Someone from MIT (sorry, I am
terrible with names) working on the basal ganglia views it (in the motor
modality) as receiving a number of motor plans/actions and allowing one to get
through (and presumably be implemented). What do you think?

|> The higher level view then is that the striatum is one place in the
|> brain where _binding_ may occur.  It seems that the info that is bound
|> here is related to motor preparation, motor sequencing, and
|> sensorimotor intergration.

So you think motor plans are actually created in the basal ganglia from
components coming from cortex, rather than the plan being constructed within
cortex? What do the cortical premotor and supplementary motor (and other frontal)
cortices do in your view, given that stimulation of these areas can cause
sequences of motor behavior and whole body postural changes? Prefrontal cortex
seems to have a strong role in the planning of action. I think the BG have more
of a role in decisions/selctions from cortical output.

|> >|> >A projection from the dopaminergic
|> >|> >midbrain perhaps provides a lower brain 'go' signal to inititate a
|> >|> >process in frontal cortex (compromised in Parkinson's). 
|> >|> 
|> >|> Probably not.  Schultz has shown that da neurons fire to trigger
|> >|> stimuli in simple tasks but when sensory events (conditional stimuli)
|> >|> are added before the trigger cue, the da cells shift to the earlier
|> >|> events.
|> 
|> >Is this not because the earlier events are important features that must be
|> >abstracted along with the trigger stimulus to form a higher level (in space/time)
|> >plan of the situation? The da cells then give a 'go' signal when the stimuli
|> >first appear and initiate the firing of the plan pattern in frontal cortex.
|> 
|> I think this has more to do with "setting the occasion" for behavior
|> than giving the go signal.

What is the difference between 'setting the occasion' for behavior and giving a
go signal to a particular behavior based on context (like the activity of the
rest of cortex, level of 'drives' from lower brain structures).

|> This assumes that the BG represent the top-level plan.  They may just
|> be working on figuring out what has happened in cortex.  Without this
|> (internal) info, planning is not possible.  

Yes, but when the BG work out what has happened in cortex, they feed the info back
to the prefrontal and premotor cortex (not the rest of cortex). Why is this? I 
propose it is to impose the integrated plan of action on the cortex.

|> >|> >There is probably a role for the two separate patch and matrix
|> >|> >systems. Interestingly, they receive input from different depths of
|> >|> >cortical layer 5. This would correspond to different stages of
|> >|> >prediction of the future in each cortical module. 
|> >|> 
|> >|> This really only holds for the prefrontal cortex and its neighbors.  
|> 
|> >OK, the time difference is only important for the higest level plans.
|> 
|> That would assume that areas like prelimbic are the source for
|> planing.  Maybe but prelimbic has diverse connections (visceral,
|> limbic).  These are anything but higher-order.

Exactly. Prelimbic (orbitofrontal cortex) is the cortical model of self. It
receives emotion/drive/motivational inputs from the hypothalamus and aminergic
brainstem nuclei via the median forebrain/cingulum bundle (maybe via
cingulate cortex), directive BG input via the thalamus, and integrates with 
highest level planning via connections to other prefrontal areas.

|> >This patch/matrix story seems complicated. Any overall idea what's happening here?
|> 
|> Different receptor systems in the two compartments; maybe different
|> regulation of a common neural circumstance (in the sense of a
|> coordinated pattern of firing).
|> 
|> The thing about the patches is that they are avoided by some areas
|> (for example, medial agranular cortex, the homologue of SMA/PMA) and

So potential plans are not sent to patches.

|> densely innervated by others (e.g., cingulate and prelimbic).

Instead the model of self sends a lot of input to them. Control? Do the BG
integrate possible plans with goals to produce action?

|> These areas are not interconnected in cortex and the are not overlapping in
|> the patches, but they might converge in the matrix.

The orbitofrontal cortex is connected to prefrontal cortex (at least according to
K+S).

|> Also, intralaminar thalamus, which projects more to striatum than to cortex,
|> only innervates the matrix.  I think then that the patches are a
|> further level of order and parcellation of inputs. 

To what purpose? What is the function of the intralaminar thalamic nuclei? Anyone
know?

|> I would say sensorimotor.  Neurons in BG only respond to things motor
|> or sensory _in the context of some task_ (in the context of some
|> strucuture).  BTW, sensory responses change with context.  In my work,
|> a neuron that responds in preparation for movement in a reaction-time
|> task may also fire to one of two tones in a tone-discrimination task
|> (in this case, tone-cued treadmill locomotion).

I would expect a center for integration of plans/states that produces a final
output plan for the individual to show an operation that was heavily context
dependent.

|> You should look up a book in the Progress in Brain Research series
|> (our libraries copy has been missing now for more than a year).  There
|> was an article on studies of pallidal lesions where people sat around
|> for hours not doing anything and then realized that so much time had
|> passed.

I'll try and find it. It reassures me after being told by someone that pallidal
lesions had been done to treat the symptoms of Parkinsons and no deficits had
been seen. That didn't seem very plausible.

|> I think the term attention is difficult to define and carries a lot of
|> baggage.  Try to be more specific about what you mean by attention.

OK: attention is the act of assigning frontal cortex to 'process' information
from a specific region/regions of cortex. Attention is where learning is
happening.

Paul



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