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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Neural Darwinism | 6/8 | https://en.wikipedia.org/wiki/Neural_Darwinism | reference | science, encyclopedia | 2026-05-05T08:31:16.671366+00:00 | kb-cron |
==== Secondary repertoire – experiential selection ==== The second tenet of TNGS regards postnatal events that govern the development of a secondary repertoire of synaptic connectivity between higher-order populations of neuronal groups whose formation is driven by behavioral or experiential selection acting on synaptic populations within and between neuronal groups. Edelman's notion of the secondary repertoire heavily borrows from work of Jean-Pierre Changeux, and his associates Philippe Courrège and Antoine Danchin – and, their theory of selective stabilization of synapses.
===== Synaptic modification ===== Once the basic variegated anatomical structure of the primary repertoire of neuronal groups is laid down, it is more or less fixed. But given the numerous and diverse collection of neuronal group networks, there are bound to be functionally equivalent albeit anatomically non-isomorphic neuronal groups and networks capable of responding to certain sensory input. This creates a competitive environment where neuronal groups proficient in their responses to certain inputs are "differentially amplified" through the enhancement of the synaptic efficacies of the selected neuronal group network. This leads to an increased probability that the same network will respond to similar or identical signals at a future time. This occurs through the strengthening of neuron-to-neuron synapses. These adjustments allow for neural plasticity along a fairly quick timetable.
==== Reentry ====
The third, and final, tenet of TNGS is reentry. Reentrant signalling "is based on the existence of reciprocally connected neural maps." These topobiological maps maintain and coordinate the real-time responses of multiple responding secondary repertoire networks, both unimodal and multimodal – and their reciprocal reentrant connections allow them to "maintain and sustain the spatiotemporal continuity in response to real-world signals." The last part of the theory attempts to explain how we experience spatiotemporal consistency in our interaction with environmental stimuli. Edelman called it "reentry" and proposes a model of reentrant signaling whereby a disjunctive, multimodal sampling of the same stimulus event correlated in time that make possible sustained physiological entrainment of distributed neuronal groups into temporally stable global behavioral units of action or perception. Put another way, multiple neuronal groups can be used to sample a given stimulus set in parallel and communicate between these disjunctive groups with incurred latency.
== The extended theory of neuronal group selection – the dynamic core hypothesis == In the aftermath of his publication of Neural Darwinism, Edelman continued to develop and extend his TNGS theory as well as his regulator hypothesis. Edelman would deal with the morphological issues in Topobiology and begin to extend the TNGS theory in The Remembered Present. Periodically over the intervening years, Edelman would release a new update on his theory and the progress made. In The Remembered Present, Edelman would observe that the mammalian central nervous system seemed to have two distinct morphologically organized systems – one the limbic-brain stem system which is primarily dedicated to "appetitive, consumatory, and defensive behavior"; The other system is the highly reentrant thalamocortical system, consisting of the thalamus along with the "primary and secondary sensory areas and association cortex" which are "linked strongly to exteroceptors and is closely and extensively mapped in a polymodal fashion."
=== The limbic-brain stem system – the interior world of signals === The neural anatomy of the hedonic feedback system resides in the brain stem, autonomic, endocrine, and limbic systems. This system communicates its evaluation of the visceral state to the rest of the central nervous system. Edelman calls this system the limbic-brain stem system.
=== The thalamocortical system - the exterior world of signals === The thalamus is the gateway to the neocortex for all senses except olfactory. The spinothalamic tracts bring sensory information from the periphery to the thalamus, where multimodal sensory information is integrated and triggers the fast response subcortical reflexive motor responses via the amygdala, basal ganglia, hypothalamus and brainstem centers. Simultaneously, each sensory modality is also being sent to the cortex in parallel, for higher-order reflective analysis, multimodal sensorimotor association, and the engagement of the slow modulatory response that will fine-tune the subcortical reflexes.
=== The cortical appendages – the organs of succession === In The Remembered Present, Edelman acknowledges the limits of his TNGS theory to model the temporal succession dynamics of motor behavior and memory. His early attempts at replication automata proved inadequate to the task of explaining the realtime sequencing and integration of the neuronal group interactions with other systems of the organism. "Neither the original theory nor simulated recognition automata deal in satisfactory detail with the successive ordering of events in time mediated by the several major brain components that contribute to memory, particularly as it relates to consciousness." This problem lead him to focus on what he called the organs of succession; the cerebellum, basal ganglia, and hippocampus.