The music goes round 'n round . . .

[From Bruce Abbott (2000.09.11.1945 EST)]

Here's something to think about:

As far as known, every area of cerebral isocortex has a reciprocal

relationship

with some part of the thalamus: that is, it receives synaptic input from

that part

of the thalamus and sends synaptic output back to that same area. Most

parts of the

thalamus have a reciprocal relationship with cerebral isocortex. (There are

a few

exceptions, such as the centromedian nucleus, which participates in a basal
ganglionic circuit.) Thus, for each functional system which involves cerebral
isocortex, there are one or more nuclei of the thalamus.

Hmmmm. Wonder what those return circuits are all about. For some reason
the term "feedback" comes to mind . . .

Thalamic lesions can and do produce cerebellar or extrapyamidal types of motor
deficits. (The pallidothalamic and dentatothalamic inputs are spatially
segregated, and synapse in different motor subnuclei.) For reasons which

remain

profoundly mysterious, lesions deliberately placed in the motor thalamus often
afford dramatic relief from some of these same motor deficits.

This probably refers to the type of thalamic operation that Michael J. Fox
underwent in an attempt to abate his Parkinson's disease symptoms. I wonder
whether there is enough information about the various connections here to
afford a closed-loop analysis.

Note: You can read the source of the above quoted material at

http://ome-web.umassmed.edu/curriculum/MBB1/MBBHTML/FB/Thalamus.html

Bruce A.

[From Bruce Gregory (2000.0912.0956)]

Bruce Abbott (2000.09.11.1945 EST)

Hmmmm. Wonder what those return circuits are all about. For
some reason
the term "feedback" comes to mind . . .

Sorry I still have found the reference you asked about. Maybe someday...
As I recall the story, the patient was suffering from an injury or
stroke that effected the neural connections from the prefrontal lobes to
the hypothalamus. He seemed perfectly normal, but had trouble "making up
his mind" after reviewing alternatives. As I recall the example was
setting his next appointment with the neurologist. When the latter
finally lost patience and set a date, the patient has perfectly happy
and had no trouble showing up at the appointed time. This example
suggested to me that the emotive centers of the brain play a key role in
"picking" from the alternatives generated by the cortex. If one were
rash enough to suggest a S-R interpretation, the alternatives each
generate an emotional response and we act on the one we "feel" most
desirable.

BG

[From Bruce Abbott (2000.0912.1755 EST)]

Bruce Gregory (2000.0912.0956) --

Sorry I still have found the reference you asked about. Maybe someday...
As I recall the story, the patient was suffering from an injury or
stroke that effected the neural connections from the prefrontal lobes to
the hypothalamus. He seemed perfectly normal, but had trouble "making up
his mind" after reviewing alternatives. As I recall the example was
setting his next appointment with the neurologist. When the latter
finally lost patience and set a date, the patient has perfectly happy
and had no trouble showing up at the appointed time.

This sounds like it could have been one of the examples cited by Antonio
Damasio (1994) in _Descartes' Error_.

This example
suggested to me that the emotive centers of the brain play a key role in
"picking" from the alternatives generated by the cortex. If one were
rash enough to suggest a S-R interpretation, the alternatives each
generate an emotional response and we act on the one we "feel" most
desirable.

Something close to this idea was offered by George E. Pugh (1977) in _The
biological origin of human values_. I think that you and Damasio and Pugh
are on to something . . . We seem almost inevitably to tag our experiences
along an evaluative dimension; without such evaluations, different options
offer no basis for choice.

Bruce A.