A critical period in neuronal development is a time of synaptic plasticity. Perineuronal Nets (PNNs) “form around neurons near the end of critical periods during development”. PNNs inhibit the formation of new connections. PNNs inhibit plasticisty. We believe this to be causal because[1] “[d]issolving them in the amygdala allowed experience to erase fear conditioning in adult rats, conditioning previously thought to be permanent.”
PNNs surround more neurons in some parts of the brain than others. In particular, “PNNs generally surrounded a larger proportion of neurons in motor areas than in sensory areas”. For example, “NNs surround almost 50% of neurons in the ventral horn of the cervical spinal cord but almost none of the neurons in the dorsal horn.” We know from other research[2] that motor control is associated with the ventral spinal cord whereas sensory input is dorsal.
PNNs are shown in green [below].
Here is a graph of PNNs in each brain region [below].
The cerebral cortex stands out as having few PNNs everywhere sampled. This makes sense if the cerebral cortex needs to be adaptable and therefore plastic. The most PNNs were discovered in the cerebellar nucleus, a motor structure.
The distribution of PNNs is evidence that motor areas are less plastic than sensory areas. If true, then sensory input may involve more computation than motor output.
The experiment in question may have also dissolved the rest of the extracellular matrix, besides PNNs, and that dissolution may have been what caused the erasure.
These are my thoughts on Distribution of N-Acetylgalactosamine-Positive Perineuronal Nets in the Macaque Brain: Anatomy and Implications by Adrienne L. Mueller, Adam Davis, Samantha Sovich, Steven S. Carlson, and Farrel R. Robinson.
A critical period in neuronal development is a time of synaptic plasticity. Perineuronal Nets (PNNs) “form around neurons near the end of critical periods during development”. PNNs inhibit the formation of new connections. PNNs inhibit plasticisty. We believe this to be causal because[1] “[d]issolving them in the amygdala allowed experience to erase fear conditioning in adult rats, conditioning previously thought to be permanent.”
PNNs surround more neurons in some parts of the brain than others. In particular, “PNNs generally surrounded a larger proportion of neurons in motor areas than in sensory areas”. For example, “NNs surround almost 50% of neurons in the ventral horn of the cervical spinal cord but almost none of the neurons in the dorsal horn.” We know from other research[2] that motor control is associated with the ventral spinal cord whereas sensory input is dorsal.
PNNs are shown in green [below].
Here is a graph of PNNs in each brain region [below].
The cerebral cortex stands out as having few PNNs everywhere sampled. This makes sense if the cerebral cortex needs to be adaptable and therefore plastic. The most PNNs were discovered in the cerebellar nucleus, a motor structure.
The distribution of PNNs is evidence that motor areas are less plastic than sensory areas. If true, then sensory input may involve more computation than motor output.
The experiment in question may have also dissolved the rest of the extracellular matrix, besides PNNs, and that dissolution may have been what caused the erasure.
Technically, the research in question concerns humans, not macaques, but I think that we are similar enough to serve as a model for macaques.