[ExI] Neuroscience Question

Anders Sandberg asa at nada.kth.se
Thu Jul 12 13:34:17 UTC 2007

Jeff Miller wrote:
> As I understand it, cell types vary significantly among the fundamental
> brain regions (cortex, cerebellum, thalamus, hippocampus, brainstem, etc).
> HOWEVER, the cerebral cortex (aka isocortex, aka neocortex), consists of
> the same neuron types, structured in a similar way, throughout. (This is
> the inspiration for one of its names, "isocortex".) That is the leading
> theory, at least --- with the exception of one neuron type (see below).

Roughly right. The cortex has nearly identical structure everywhere, with
the same six layers, apparently the same local circuit diagram, the same
kinds of neurons and so on. BUT there are small variations between
cortical regions. The most famous one is the Band of Gennari, a whitish
line in layer  4C of primary visual cortex due to the high prevalence of
myelinated axons from the lateral geniculate nucleus. Motor cortex has
some very large-bodied pyramidal cells (Betz cells) that are not found

The classic brain areas defined by Brodmann were defined based on
differences in cytoarchitecture; they seem to fit functional areas
surprisingly well, but there is a lot of individual variability.

My own guess is that we have a basic circuit that adapts depending on what
kinds of connections and input signals it gets, and this adaptation can
change cell numbers, types and function quite profoundly.

Anders Sandberg,
Oxford Uehiro Centre for Practical Ethics
Philosophy Faculty of Oxford University

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