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A Neural Theory of Mind

Paul Bush paul at phy.ucsf.edu
Tue Apr 23 19:16:57 EST 1996

In article <4lhhuj$7tj at eis.wfunet.wfu.edu>, laubach at biogfx.neuro.wfu.edu (Mark Laubach) writes:

Thanks for your very informative post, you obviously know a lot about this system.
Therefore, could you write a single paragraph that sums up your opinion of the
function/operation of the basal ganglia? Just a high level idea. Your hunch, gut
feeling on the subject. Doesn't matter if some bits are wrong - speculate a
bit, This would be incredibly useful to me.

Specifics - Please point out where I am wrong here:

|> paul at phy.ucsf.edu (Paul Bush) wrote:
|> >I don't have a good understanding of how the basal ganglia
|> >work. Basically, though, the striatum appears to be a lateral
|> >inhibitory network designed for filtering out input patterns
|> >(compromised in Huntinton's). 
|> Maybe.  The evidence for an effect of one spiny neuron on its
|> neighbors is lacking despite a good bit of effort to find it (see
|> Jaeger and Wilson in J. Neurophysiol last year).  Many modellers have
|> incorporated the notion of lateral inhibition into their models of the
|> basal ganglia.  In fact, a paper from my lab argued that this
|> circuitry gives rise to a form of working memory (Woodward et al. in
|> the Houk book).  The best evidence for this to date comes from studies
|> of striatal interneurons (see stuff by Kita, Kawaguchi, Plenz).
|> Still, the jury's out on this one ...

Yes, I think working memory is a good label. Interestingly, I now think that
cortex is also a big laterally inhibitory network.

|> >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.

|> The exaxt role of the da signal is yet to be clarified.
|> Also, it should be pointed out that the standard bit about da and the
|> striatum is based on the rat.  In primates, da neurons innervate all
|> areas of cortex (see paper from Kaas' lab last year in JCN).

So the reward signal in primates is more widely distibuted. In rats it just says
yes/no to the top-level plan.

|> >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.

This patch/matrix story seems complicated. Any overall idea what's happening here?

|> >The basal ganglia assign processes to high level frontal cortex (attention)
|> >which has reciprocal relationships with the limbic cortex, which as
|> >described previously is the model the brain makes of itself -
|> >consciousness. In this way consciousness is integrated with perceptual state.
|> The best evidence for the role of the bg in the control of behavior
|> comes from studies of reaction-time performance. 

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