Forward Dendritic Spikes - Advancing Artificial Intelligence Through Biological Process Applications - page 53

terns that resulted in full-forward propagation,
while local spikes that were scattered over 2 ms
or more yielded pseudosaltatory conduction or
aborted apical shaft spikes.

The synaptically excited branch (as16a) fired a
local spike that passively propagated into the
apical shaft (vertical dashed line 1) originating a
step-like increase (arrow a) in the EPSP envelope.
Although the apical shaft failed to initiate an AP,
it still carried enough current to initiate a local
spike in a non-excited branch (as12) because of
the lower threshold of thinner branches. In turn,
this local spike fed current back into the apical
shaft originating a new spikelet (vertical dashed
line 2). The spikelets were smoothed out during
their passive propagation to the soma (arrows
b), adding to the EPSP envelope. Thus, though
local spikes at positions distant from the soma
cannot be discriminated by somatic recordings,
they contribute notably to the EPSP envelope.
This phenomenon facilitates branch-to-branch
saltatory activation toward the soma, even when
the common parent apical shaft was conducting
an aborting spike. An analogous conduction was
earlier postulated between adjacent active spines
(Miller et al ., 1985). The apical shaft would thus
serve as a reservoir of electric charge enabling the
firing of non-activated branches, which in turn

Dendritic Chattering by
Cross-Spiking: An Internal
Language between Dendrites

A closer look into the details of the local integration
of dendritic spikes revealed a notable mechanism.
Local spikes initiate not only in synaptically
activated branches, but also in adjacent ones via
apical shaft ( cross spiking ). The number of these
branches that fired “sympathetically” varied con-
siderably depending on the initial settings. This
mechanism facilitates forward conduction due to
the successive current injections delivered into the
apical shaft by local spikes at sites progressively
nearer to the soma in a cascade-like manner.
The mode in which the lateral dendrites and
the apical shaft interact is better appreciated in
an example of subthreshold activation that initi-
ated a small number of local spikes (Figure 3).

Figure 3. Cross-spiking: An internal language between dendrites. Explanation in the text. Modified from
Ibarz et al., 2006.

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