Forward Dendritic Spikes - Advancing Artificial Intelligence Through Biological Process Applications - page 51

Figure 1. Forward propagation of spikes: Loudspeaker effect of moderately flaring active cables. When
the spike travels in a cable of constant diameter (left) the current remains stable. In flaring active cables
(right), the spike initiated in the narrow edge travels forward with increasing transmembrane current
that ensures propagation.

The precise distribution of some channels also
had a profound effect on the site of initiation that
depended on third variables.
Maybe, the most important conclusion of our
study is that there are too many variables with
a strong influence on the site of spike initiation
within their recognized experimental ranges of
variation. In fact, the activation mode varied
extremely when two or more variables were cross-
analyzed, becoming rather unpredictable when
all the variables were considered. An example
is illustrated in Figure 2 that shows multiple and
variable activation modes in a cross-analysis of
four variables, input strength, input locus, strength
of inhibition, and dendritic gradient of potassium
channels.
One notable observation is that spike initiation
in the apical shaft does not necessarily lead to cell
output when certain parameters are combined, a

result verified by experimental observations us-
ing synchronous activation (Canals et al ., 2005;
Golding & Spruston, 1998). In the model, the spike
could either be aborted within the apical shaft or
“jumped” into the axon, backpropagating from
there into the apical dendrite, i.e. the so called
pseudosaltatory mode. It should be noted that this
mode of conduction may easily go undetected in
experiments. Even with dual intracellular record-
ings from the soma and the apical shaft, data can
be erroneously interpreted as a continuous forward
propagation or backpropagation, depending on
whether the dendrites were impaled at the firing
or the refractory zones of the apical shaft. Ex-
amples of even more complex modes of forward
propagation consisting of a spatial sequence of
decremental and regenerative spike have been
shown in neocortical pyramidal cells that have
longer apical shafts (Larkum et al., 2001).