Synaptic plasticity/dysplasticity, process memory and item memory in rodent models of mental dysfunction

Abstract

Activity-dependent changes in the effective connection strength of synapses are a fundamental feature of a nervous system. This so-called synaptic plasticity is thought to underlie storage of information in memory and has been hypothesized to be crucial for the effects of cognitive behavioral therapy. Synaptic plasticity stores information in a neural network, creating a trace of neural activity from past experience. The plasticity can also change the behavior of the network so the network can differentially transform/compute information in future activations. We discuss these two related but separable functions of synaptic plasticity; one we call "item memory" as it represents and stores items of information in memory, the other we call "process memory" as it encodes and stores functions such as computations to modify network information processing capabilities. We review evidence of item and process memory operations in behavior and evidence that experience modifies the brain's functional networks. We discuss neurodevelopmental rodent models relevant for understanding mental illness and compare two models in which one model, neonatal ventral hippocampal lesion (NVHL) has beneficial adult outcomes after being exposed to an adolescent cognitive experience that is potentially similar to cognitive behavioral therapy. The other model, gestational day 17 methylazoxymethanol acetate (GD17-MAM), does not benefit from the same adolescent cognitive experience. We propose that process memory is altered by early cognitive experience in NVHL rats but not in GD17-MAM rats, and discuss how dysplasticity factors may contribute to the differential adult outcomes after early cognitive experience in the NVHL and MAM models.

Learning to learn persistently modifies an entorhinal-hippocampal excitatory-inhibitory subcircuit

“…If the changes in neural circuit function caused by CCT are due to acquiring a content-specific place avoidance memory then learning an additional place avoidance should cause additional changes, whereas if the neural circuit changes result from the "process memory" of learning to learn 21 then the additional training should not cause incremental neural circuit changes. A new group of mice (n=5) received initial CCT and after the 1-week retention test, they received subsequent CCT to acquire a different place avoidance memory either in the same environment followed by CCT in a novel environment (n=2), or in counterbalanced order (n=3) to control for the sequence.…”

Evidence of Hyperacusis in Adult Rats Following Non-traumatic Sound Exposure

“…One such vulnerability is the opportunity for maladaptive plasticity, which refers to structural or functional nervous system changes that disrupt normal function. Dysplastic symptoms such as hyperexcitation, altered neural connectivity, and topographic reorganizations can interfere with perceptual discrimination (O’Reilly et al, 2019), cause hypersensitivities or phantom percepts (Flor et al, 2001; Costigan et al, 2009; De Ridder et al, 2011), and contribute to chronic pain (Kuner and Flor, 2016). In the central auditory system, maladaptive plasticity is thought to underlie the generation of auditory disorders including chronic tinnitus and hyperacusis, the uncomfortable sensations of ringing in the ears and sound hypersensitivity.…”

Lactate: A Novel Signaling Molecule in Synaptic Plasticity and Drug Addiction

“…Activity‐dependent synaptic plasticity, which means changes in the strength of the connection between neurons, is usually regarded as the neural basis of the formation and storage of memory . Moreover, dysfunction of synaptic plasticity has also been linked closely to the pathophysiology of early‐phase Alzheimer's disease and mental disorders such as schizophrenia . Synaptic plasticity is usually divided into functional synaptic plasticity related to transmission efficacy and structural plasticity concerning storage of information (see Box for more details).…”