Hippocampus: The dentate gyrus
reinterpreted as a creator of new cell assemblies in CA3
The dentate gyrus contains a number of cell
types radically different from most other cells in the brain.
These include the granule cells, whose terminals on CA3 pyramids and
mossy cells are not NMDA receptor dependent, and are so powerful that a
single mossy terminal can fire its postsynaptic cell.
In this project several of the unusual features of the dentate
network are being re-interpreted as serving the special set of criteria
necessary in cell assembly formation, in which sets of granule cells single
out sets of CA3 cells to be subsequently linked up and assigned to mental
Long-term memory: Molecular mechanisms
supporting memory storage and recall The traditional
view which describes memory as the pattern of synaptic weights and nothing
else fails to account for the fact that the typical cortical synapse only
survives for about three months.
In addition, when one carefully calculates the amount of information
that can be reliably stored in a network of neurons held together by nothing
other than synaptic weights, one finds that it is many orders of magnitude
smaller than required by the vast capacity of actual brains.
This brings up the need for molecular mechanisms to act in tandem
with synaptic memory, so as to permit placing large sets of synapses into
storage, as units, and retrieve them later on demand.
As it turns out, the memory-supporting molecules, unlike the ones
envisioned in the old “memory molecule papers” from fifty years ago, do not
need to be large, as they only need to have enough information capacity to
act as unique identifiers able to point to the individual stored mental
Visual cortex: Shape perception
The old cell assembly hypothesis of Hebb can be updated to
account for syntactic relations between igniting cell groups.
Co-ignitions between pairs and triplets of cell assemblies can form
rudimentary “sentences” which can be joined on their shared “noun” elements
(such as nodes), and together form linked structures of arbitrary
complexity. Such structures are
suitable for conveying visual shape information within the brain.
Legéndy C. R. (2015)
Molecular mechanisms of long-term recall.
Columbia Univ. Psych. Dept. internal communication October 1, 2015.
Legéndy C. R. Circuits in the Brain: A model of shape
processing in the primary visual cortex. (Springer, 2009).
Legéndy C. R. and Salcman M. (1985) Bursts
and recurrences of bursts in the spike trains of spontaneously active
striate cortex neurons. J. Neurophysiol. 53, 926-939.
Legéndy C. R. (1967) On the scheme by which
the human brain stores information. Math. Biosciences 1, 555-597.
Early papers (on helicons): http://heliconrefs.com/