Big brain evolution: learning new tasks (Evolution)

by David Turell @, Saturday, April 21, 2018, 21:55 (922 days ago) @ David Turell

Changing how to do a simple task results in reuse of existing systems of neurons:

"The hallmark of intelligence is the ability to learn. As decades of research have shown, our brains exhibit a high degree of “plasticity,” meaning that neurons can rewire their connections in response to new stimuli. But researchers at Carnegie Mellon University and the University of Pittsburgh have recently discovered surprising constraints on our learning abilities. The brain may be highly flexible and adaptive overall, but at least over short time frames, it learns by inefficiently recycling tricks from its neural repertoire rather than rewiring from scratch.


"Several years ago, Yu, Aaron Batista of the University of Pittsburgh and members of their labs began using brain-computer interfaces (BCIs) as tools for neuroscience discovery. These devices have a chip roughly the size of a fingernail that can track the electrical activity of 100 neurons at once in the brain’s motor cortex, which controls movement. By monitoring the sequences of voltage spikes that run through the individual neurons over time, a BCI can calculate a “spike rate” to characterize the behavior of each neuron during the performance of a task.


"When Yu, Batista and their colleagues monitored the motor cortex of a monkey while it repeatedly performed simple arm-waving tasks, they found that the neurons were not firing independently. Rather, the behavior of the 100 neurons being measured could be described statistically in terms of about 10 neurons, which were variously exciting or inhibiting the others. In the researchers’ analysis, this result showed up as a set of plotted points that filled only a small volume of a 100-dimensional data space.

“'We’ve been calling [that volume] the intrinsic manifold because we think it’s something really intrinsic to the brain,” said Steven Chase, a professor of biomedical engineering at Carnegie Mellon. “The dimensionality of this space is highly predictive of what these neurons can do.”


"To find out, the researchers first let primates equipped with BCIs become adept at moving the cursor left and right. Then the team switched the neural activity requirements for moving the cursor and waited to see what new patterns of neural activity, corresponding to new points in the intrinsic manifold, the animals would use to accomplish them.


"But to the researchers’ surprise, neither realignment nor rescaling occurred. Instead, the researchers observed a highly inefficient approach called “reassociation.” The animal subjects learned the new tasks simply by repeating the original neural activity patterns and swapping their assignments. Patterns that had previously moved the cursor left now moved it right, and vice versa. “It’s recycling what they used to do,” Golub said, but under new circumstances.

"Batista suggests that the changes in the synaptic connections between neurons that would be required for realignment may be too hard to accomplish quickly. “Plasticity must be more limited in the short term than we thought,” he said. “Learning entails forgetting. The brain might be reluctant to let go of things it already knows how to do.”

"Chase likened the motor cortex to an old-fashioned telephone switchboard, with neural connections like cables linking inputs from other cortical areas to outputs in the brain’s cerebellum. During their experiments, he said, the brain “just rearranges all the cables” — though the nuances of what that means are still unknown.

“'The quick-and-dirty strategy is to change the inputs to the cortex,” Yu said. But he also noted that their experiments only tracked the brain’s activity for one or two hours. The researchers can’t yet rule out the possibility that reassociation is a fast interim way for the brain to learn new tasks; over a longer time period, realignment or rescaling might still show up."

Comment: this is a study of the motor cortex only, and it shows the immediate result is re-use of existing neuronal patterns. No size change. The point about possible brain enlargement is that implementation may be planned in the frontal cortex, but must take place elsewhere such as the motor cortex with coordination in the cerebellum. The pre-frontal and frontal cortex (the thinking cortex) are where all the enlargement has taken place from Lucy to us. The motor cortices, the sensory cortices are little changed in size thru evolution, nor is the hypothalamus or cerebellum. Thinking of a new concept and the planning for it is where all the enlargement has taken place. Implementation uses the other areas mentioned. Again to avoid criticism, this is how the s/s/c interfaces with the brain.

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