A Neural Theory of Mind
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
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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