a thinking brain

r norman rsn_ at _comcast.net
Fri Jun 25 21:40:25 EST 2004

On 25 Jun 2004 18:58:59 -0700, rscanlon at nycap.rr.com (ray scanlon)

>Fictive motor programs.
>Fundamental to our design of a brain that thinks is the halting of a
>motor program at the ventral anterior-ventral lateral complex of the
>thalamus. What shall we call such a halted and rejected motor program?
>Some have bridled at calling it any kind of a motor program. They say
>that if it isn't connected to motor neurons it isn't a motor program
>This awkwardness is apparent in the study of central pattern
>generators. The preparation is usually a small neural circuit
>maintained in vitro. After studying the output of the neurons, the
>investigator says that if this circuit were re-connected to the body
>(a leech, say), the organism would swim. The re-connection remains
>hypothetical and this is unsatisfactory to some. No matter how
>sophisticated the argument may be that the circuit would work, people
>ask for a demonstration. In only a few cases, has this been possible.
>We believe wholeheartedly that it would, but doubts persist. The motor
>pattern produced by the circuit is called a fictive motor pattern.
>I argue that we should call the motor programs that are halted and
>rejected at the thalamus "fictive", fictive motor programs. There
>should be no element of implied falsity. I feel that the motor
>program, although it disappear into thin air, is real, and if it were
>to continue to the motor cortex, the animal would behave.

The term "fictive behavior" is already in use, usually describing
nervous activity that would ordinarily produce behavior except that
the nervous system has been disconnected from the effectors.  

The problem of talking about some premotor activity somewhat removed
from the motor neurons is the very real possibility that spinal
circuits may play a major role in shaping and refining the final
activity, not to mention modulating it or even gating it completely.
It is hard to know exactly what actual behavior would result from that
activity.  That is why there is a reluctance to call it motor
behavior, fictive or  not.

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