Essay On Polychronization

POLYCHRONIZAT ION
There has been recent experimental evidence that neurons can transmit information through precisely timed spike patterns. Patterns can be found in the precise spike timings of a group of neurons, which form a functional neuron group. Polychronization [20] can be defined as the ability to produce ‘time-locked’ but not synchronous firing patterns with milli-second precision. A network consisting of a group of neurons recurrently connected, with axonal delays and a synaptic efficacy tuning technique called Spike-Timing-Dependent Plasticity
(STDP) can be shown to display polychronization.
A simple example of polychronization is depicted below.
Figure 6.1: Polychronization[20]
The figures above depict polychronous activity among a network of neurons. (A) depicts
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Even when no external input stimuli are presented to the network, polychronous groups emerge. This shows that the network is capable of generating random memories even without prior experiences.
However, when certain common input stimuli are repeatedly presented to the network, and STDP is allowed to run on the network, we can observe the presence of subgroups that are activated every time the corresponding stimuli is presented to the network. Another interesting property is that different polychronous groups are built corresponding to different inputs even when all the inputs are presented to the same set of input neurons.
As an example, 2 different inputs are presented to a network as different sets of spike timings. Initially, there are no distinct groups, but as STDP is allowed to run on the network, groups begin to develop.
When the network settles down, we observe that the presence of the above stimuli will give rise to the same set of polychronous groups.
This can be thought of as the development of memory within a network based on previous experiences. We can also see that, as different inputs are introduced and the network is made to learn these

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