Biomedical Engineering Reference
In-Depth Information
1
2
Stimulus
current
Spike
interval
variance
1
2
Time
Figure 6.9
Type 1 and type 2 dynamics shift to high variance at different points in a noisy tran-
sient stimulus (top). Type 1 neuron switches to high variance when mean stimulus
current level is above the threshold level (
), while type 2 neuron switches when
mean stimulus is below threshold.
content is raised, so that more time is spent poised in the late high-variability stage
of firing. This figure also illustrates the high variability associated with slow motion
just above threshold, discussed above.
NMDA channels are highly regulated by their subunit expression, by phosphoryla-
tion, by extracellular glycine levels, and by factors such as intracellular polyamines
and pH [50]. Thus it is likely that the precision and reliability of spiking is con-
stantly being tuned by modifying the balance between AMPA and NMDA receptor
activation at excitatory synapses.
6.8
Class 1 and class 2 neurons show different
noise sensitivities
The manner in which the switch between early and late stage variability happens,
depends on the threshold behaviour of the neuron. There are two major classes of
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