Biology Reference
In-Depth Information
Table 1
The number of effective responses changes with different delays
Non-delayed
0.01s delay
0.05s delay
0.10 s delay
165% baseline
10
10
3
2
185% baseline
9
9
9
9
210% baseline
9
9
8
0
Fig. 5. Effects of delays when signals are sparse. Lower panel: Train of 10 signals with
w
1
=
0.01s,
w
2
=
0.2s and
bolus
=
20. Upper panel: DA-e responds in the form of 10 separated peaks. Different delays (corresponding to those in Fig. 4) result
in some smoothing in the responses, but the peaks remain separated.
of neurons. For instance, if the threshold in Fig. 5 is 165% of the baseline value, the non-delayed system
has ten effective responses (as seen in separable peaks above the threshold line), among which one lasts
for 0.07s and the other nine between 0.15s to 0.2s. By contrast, when the dopamine release is delayed
by 0.1s, the system only fires twice: once for 0.17s and once for 1.7s. The abnormally long second peak
is the result of merging peaks and the fact that the last eight responses do not fall below the threshold.
As a second scenario, suppose that the threshold is 210% of the baseline. In this case, the non-delayed
system fires nine signals, lasting from 0.02s to 0.04s, whereas there is no effective response at all when
delay is 0.1s. Some representative results are summarized in Table 1. While these results show that
delays may affect signaling accuracy, one should also note that the system does retain its signaling
capacity if the delay is relatively short (such as 0.01s in our simulations) and if the threshold is positioned
differently, for instance, at 185% of the baseline value.
Effects of stochastic noise
Signal transduction in the dopamine system depends on the attachment of vesicles to the presynaptic
membrane and their subsequent release of dopamine into the synaptic cleft [24]. Of course, the intra-
cellular environment is heterogeneous, and changes in metabolic state, temperature, and pH, as well as
