Effects of a classical conditioning paradigm on hind-limb flexor nerve response in immobilized spinal cats.

Abstract

Cats were maintained on Flaxedil after spinal transection at T-12 under ether anesthesia. Experimental animals were classically conditioned by electrical stimulation of the exposed superficial peroneal nerve (CS), paired with cutaneous shock to the ankle of the same limb (US). The CR was the gross efferent volley recorded from the exposed deep peroneal nerve. Control animals were divided into unpaired CS and US, CS-only, and US sensitization groups. Results showed that the experimental conditions produced increases in the amplitude of the gross efferent volley while unpaired CS and US, and CS-only control conditions produced no change or a decrease in amplitude. The US sensitization group showed that no sensitization was present at the intertrial intervals used in experimental conditions.Spinal "conditioning" has a long and controversial history, due in part to the earlier belief that learning is the special province of the cerebral cortex and in part to contradictory empirical findings. Shurrager and Culler (1940) first reported successful classical conditioning of a spinal flexion response in acute spinal waking dogs. Utilizing a weak tail-shock conditioned stimulus (CS) and a hindpaw-shock unconditioned stimulus (US), paired trials produced responding to CS while unpaired and CS-alone trials did not. Subsequently, several studies by Kellogg and associates (Kellogg, Deese, Pronko, & Feinberg, 1947;Kellogg, Pronko, & Deese, 1946) failed to verify the Shurrager and Culler (1940) results. However, the Kellogg studies also failed to replicate many, essential features of the Shurrager investigations. Kellogg and associates utilized chronic preparations and presented CS and

Learning from the spinal cord: How the study of spinal cord plasticity informs our view of learning

“…This aspect of the work has not proven replicable and subsequent research has routinely used CSs that generate a CR-like (alpha) response prior to training. Acknowledging this limit, Thompson and his colleagues refined the paradigm with the aim of developing a model system to study the neurobiology of learning within the mammalian central nervous system (CNS; Fitzgerald & Thompson, 1967; Patterson, 1976, 2001; Patterson, Cegavske, & Thompson, 1973). In a typical experiment, electrical stimulation of the thigh or a nerve (e.g., the saphenous) served as the CS.…”

In Search of Memory Traces

“…Because of our success in using spinal reflexes for analysis of habituation we tackled classical conditioning of the flexion reflex in the acute spinal animal, with some success (Patterson et al 1973). However, I concluded it was not a good model of associative learning in the behaving mammal.…”

“…Gabriel draws the following rather strong conclusion: "clearly the bias In the late 1960s and early 1970s we tried several different types of model systems to analyze neural substrates of mammalian associative learning and memory. Because of our success in using spinal reflexes for analysis of habituation we tackled classical conditioning of the flexion reflex in the acute spinal animal, with some success (Patterson et al 1973). However, I concluded it was not a good model of associative learning in the behaving mammal.…”

Exposure to intermittent nociceptive stimulation under pentobarbital anesthesia disrupts spinal cord function in rats

“…Central sensitization produces a lasting increase in behavioral reactivity that has been linked to the development of neuropathic pain (Treede et al 1992). Other studies showed that spinal cord neurons are sensitive to stimulus (Pavlovian) relations (Fitzgerald and Thompson 1967;Patterson et al 1973;Beggs et al 1983) and that the vigor of a spinal reflex is modified by its consequences (instrumental learning; Buerger and Fennessy 1970;Chopin and Buerger 1976;Grau et al 1998). These effects appear to be mediated by some of the same neurochemical mechanisms implicated in neurobiological models of learning and memory within the brain (Harris et al 1984;Morris et al 1986).…”

“…Recent studies have challenged this perspective, demonstrating that spinal cord neurons can support some complex behaviors (e.g., stepping) and simple forms of learning (Fitzgerald and Thompson 1967;Buerger and Fennessy 1970;Patterson et al 1973;Chopin and Buerger 1976;Beggs et al 1983;Edgerton et al 1992;Grau et al 1998). An example of spinal learning is observed in the pain system, where stimuli that engage pain (nociceptive) fibers can sensitize spinal neurons, a phenomenon known as central sensitization (Woolf 1983).…”