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Advanced Neurology Evaluating plausibility of thalamic model

Figure 1. The two primary types of transmission relays of the thalamus. First-order relays (left) receive subcortical sensory and motor inputs, along with
inputs from the reticular formation, projecting to the primary areas of the cortex. Higher-order relays (right) receive inputs from layer V of the cortex and
the reticular formation, forming a trans-thalamic pathway that retransmits information within the cortex from one area to another. Adapted from Zhu and
Lo and updated based on Sherman. Copyright © 1999 Society for Neuroscience.
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are computationally equivalent. 16,19,28 This equivalence has behave such as axons, retrogradely conducting potentials
been empirically observed in experiments reconnecting generated at the interneuron soma. Within the triad, the
the inputs of the lateral and medial geniculate nuclei relay dendrite combines the excitatory input from the
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and demonstrates a pluripotent processing capacity of the sensory axon with the GABA-A inhibitory input from
thalamus relatively independent of the input. the interneuron AD. This combination results in the
The thalamus consists of two layers (Figure 2). The first normalization of the sensory input, arriving at the triad,
layer, responsible for receiving sensory inputs, comprises a where this input is divided by the overall sum of inputs.
pool of relay neurons (REs) intermingled with inhibitory This operation aligns with the divisive effect of GABA-A
interneurons. The second layer, known as reticular synapses – only GABA-A synapses are found in ADs,
neurons (Rs), receives excitatory input from the first layer while GABA-B synapses, which have a subtractive effect,
and demonstrates synchronized oscillatory behavior in are absent from AD appendages. In addition, metabotropic
their membrane potentials, 22,30 attributed to their dendro- glutamate synapses between sensory axons and ADs
dendritic contacts and specific conductances. The neural function as a biological switch, amplifying signals from
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appendages of these three types of neural components arriving interneurons until GABA-A synapses become
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converge at triads: (i) an excitatory sensory axon terminal; functional.
(ii) an interneuron dendrite functioning as an input/output In the computational systemic context of neural
structure, receiving excitatory input from the sensory axon circuitry, the thalamus would organize input patterns into
terminal and producing inhibition in a relay dendrite; and axes and orthogonal coordinates corresponding to their
(iii) a relay dendrite that receives excitation from the sensory PCs, enabling a unified form of neural code throughout
input and inhibition from the interneuron dendrite. The the entire cortex. 8,11,12 Its cytoarchitectural organization
centrally represented interneuron possesses axoniform into two layers closely resembles a folded auto-associative
dendrites (AD). This unconventional morphology neural network for dimensionality reduction through PC
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supports the hypothesis that interneuron dendrites may extraction (Figure 3). This type of neural network is capable

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