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Advanced Neurology Evaluating plausibility of thalamic model

connections of the Rs for approximately 100 ms, the burst It is worth noting that in the experimental setup of
firing mode of these neurons will be triggered. These Kim and McCormick, O represents the artificial input
j
12
components will be relayed to the cortex in burst mode, applied to the Rs. The sustained inhibition effect over time,
where they will be integrated into neuron populations that as indicated by the prolonged tails of the Rs responses
are hierarchically more abstract. 8,53,54 in Figure 6, was modeled using the following function
Therefore, the modulation and shaping of the (Equation VIII):
reticular activity are crucial for determining the order y x 1 e x (VIII)
log
2
of PC extraction, and their sequence of activation plays
a key role in encoding thalamic input properly into
the cortex. Demonstrating that the activity of these Where y corresponds to the response of the Rs (mV)
artificial neurons mirrors electrophysiological findings and x to time (ms).
is a fundamental step in validating the system. One Across all tested frequencies, we observed consistent
study that effectively outlines the electrophysiological numbers of responses from Rs (Figure 8; green line),
properties of Rs activity is conducted by Kim and dependent on the utilized frequency and time interval
McCormick. In this study (Figure 7), they evaluate the (Figure 8; grey line). The response of REs also exhibited
57
effects of inhibitory summation and facilitation resulting progressively increasing sustained inhibition with higher
from high-frequency stimulation of the perigeniculate stimulation frequencies.
Rs over the dorsal lateral geniculate nucleus REs. When It is important to note that we were only able to achieve
potentials are generated at a frequency exceeding 100 Hz, results similar to those of Kim and McCormick through
57
the amplitudes of the first four to six post-synaptic the use of our specially designed probabilistic pre-synaptic
inhibitory potentials (arrows) progressively increase, Hebbian learning rule (Equation 8), although we do not
followed by individual potentials of reduced amplitude. completely understand the biological reasons. This suggests
The authors argue that the exponential increase in the that potential mechanisms for the facilitation of inhibitory
amplitude of the inhibitory response could only occur if synapses are somehow involved with plasticity/learning
there were also mechanisms facilitating such a synaptic mechanisms. Recently, there has been an increasing
response.
acceptance of such interpretations in neuroscience and our
In Figure 8, we depict the results of our model findings are consistent with the literature. 58
replicating the same stimulation scenario as in the Another crucial aspect of reticular activity is the
experiment conducted by Kim and McCormick. To sculpting of the response waveform. Rs exhibit a slow
12
replicate the inhibitory facilitation mechanism, we tested synchronous basal oscillation (<15 Hz), generated by
two modified versions of our pre-synaptic probabilistic shared gap junctions among them. 16,28,51 This oscillatory
Hebbian learning rule. The first one was presented early, activity effectively promotes coordinated firing during
and the second one was specially designed to emulate the competitive activity and establishes a maximum time
experimental stimulation conditions (Equation VII): interval for the stimulation of REs (approximately 100 ms).

j
i
W RO W (VII) This period is essential for determining the number of Rs
ji
A B

C D

Figure 7. Summation and facilitation in perigeniculate reticular neurons to dorsal lateral geniculate nucleus relay neurons synaptic transmission. At
frequencies exceeding 100 Hz, action potentials lead to a progressive increase in the amplitudes of the first four to six inhibitory post-synaptic potentials
(IPSPs), followed by subsequent IPSPs with diminished amplitude. The number above each trace denotes the average frequency of action potential
discharge. The distance between the arrows increases as the amplitude of the wave increases. Copyright © 1999 Society for Neuroscience.

Volume 3 Issue 3 (2024) 9 doi: 10.36922/an.3188