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A notation for intracortical neural connections

by Gideon Kowadlo and David Rawlinson

In a previous post (section ‘Regions’), we discussed the distinction between cortical layers and levels. The literature often describes connections between cortical layers in one level to cortical layers in another level. We are not aware of a written convention for this purpose and propose one here.

The basic form describes the direction of signal transmission from the location of the soma (cell body) to the efferent synapse (where the nerve connects to another nerve or motor unit), separated by an arrow. One statement should be used per neuron.

soma  →  efferent synapse

The location is specified by:

H[n]:C[i], where:

H[n] = hierarchy level n
C[i] = cortical layer i

If one neuron branches and terminates in two locations, they are comma separated. Where these are co-located in the same Hierarchy Level, the subsequent Level specifier is omitted for brevity.

e.g. Referring to the figure in the section ‘Regions’ in the aforementioned post, the FF direct pathway can be described as follows:

H[n]:C[5] → H[n+1]:C[4], C[2/3]
Dendrites are specified by prepending d[i]. Using the same example, it would be more complete as:

H[n]:d[2/3]C[5]→H[n+1]:C[4], C[2/3]

Importantly, this convention is easy to type in to any text editor. Arrows can be typed with standard keyboard characters hyphen and greater than symbol “->”. Also, many word processors will convert an arrow with two hyphens to a special arrow character i.e. “–>”.

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