Thursday, April 18, 2013

Notes on Our Tenth Meeting

We read a paper discussing a body machine interface (BMI) involving macaques who learned to manipulate a mechanical arm via implanted electrodes. Here is some of what we talked about.

Does the BMI involve a physical connection with the brain?

There are different methods of measuring brain activity, with different profiles in terms of temporal and spatial precision. This one used implanted probes measuring electrical activity. This has the disadvantage of killing or damaging brain tissue.

Multi unit recorders last longer than single unit recorders.

They also showed that larger samples were yielding more accurate predictions.

They show that brain activity is not as localized as previous models suggest—at least with respect to these tasks.

The event of an individual cell firing seems to be important, even though no one cell or set of cells is always implicated in a specific behavior and different cell units can underwrite the same behavior. We just don't know enough about what is going on in every case: we don't always know if there is redundancy; we don't always know if the cells firing in a given case are merely transferring information, as opposed to originating a sequence of information transfer; etc.

3 things:
1.     the brain does not always make up for missing parts.
2.     Redundancy: multiple sets of neurons that perform (roughly) the same function
3.     Plasticity: the remaining parts of the brain re-learn how to do stuff (that they were not engaged in previously)
Age, etc. matters for plasticity (e.g., infants having half of brain removed but developing relatively normally)

Ablation studies: they inject something really nasty in the brain to kill a local area of neurons. They then want to say that killing these neurons had some effect, so we can infer that this region does certain thing. But this only underwrites inferring that the relevant area is implicated in the process that issues in the behavior, but not that the behavior originates in or is localized there.
It’s much easier to establish that a region is not necessary for something than that it is sufficient for something.

An interesting portion of the 'Discussion' section of the paper noted this: The way the brain learns to use the artificial arm is by engaging with it and using it, and this engagement and use does not rely on the same informational inputs as in the normal case. In the case where there is an artificial arm, there is no proprioceptive input, just the informational input from vision and the representation of the goal. The brain is shaped by the way that it receives information about the location of the arm and by the goals of the situation. This is interesting because it makes the representation of the goal more relevant to brain structure once the input from proprioception is eliminated.

Proprioception is important in the normal case, but it is not essential. The brain can still learn and manipulate in the absence of input from proprioception. Then the representation of the goal becomes more important than in the normal case.

But: Is vision part of proprioception?

Not ‘proprioception’ in the technical sense. This references a specific set of nerves that are responsive to stretching, firing more when stretched and less when not. How much they are stretched usually depends on the positioning of your limbs.

This is interesting in relation to issues raised by the work of Merleau-Ponty and others. The exciting part here is that there is evidence of informational input to action (in the normal case) that comes from the body to the mind controlling the action.

2 questions:
1.     What part of the brain is causing the body to move?
2.     Why someone did something, where this is given in terms of the mind, conceived of differently than just as identical to the brain.

The important idea for the M-P picture is that inputs and outputs are not distinct and distinctly directional in the way that the Cartesian picture (ghost in machine) envisions.

There is a connection here to old-school cybernetics, understood as the rigorous studying of machines as information transforming systems. A machine is something which takes a vector of information as input and produces a vector of information as output. A machine transforms a vector of information.
On this view, there could be no ghost distinct from the machine.

(Now, cybernetics means something like the study of all computer science, or implanting devices into the human body.)

This view entails that anything that the body responds to becomes a part of the system, which seems to be a claim that M-P would like.

From the biologist’s point of view is it important to distinguish between where you end and where the car begins. Form this perspective, BMI is better thought of as brain expansion. But there are other points of view that do not see it as necessary to make this distinction.

No comments:

Post a Comment