NEUROBIOLOGY OF LEARNING AND MEMORY 67, 64–68 (1997) ARTICLE NO. NL963736 BRIEF REPORT Evidence for Spinal Conditioning in Intact Rats ROBIN L. JOYNES,PAUL A. ILLICH, AND JAMES W. GRAU 1 Department of Psychology, Texas A&M University, College Station, Texas 77843 1975; Fitzgerald & Thompson, 1967; Grau, Salinas, Prior work suggests that spinal systems are sensitive Illich, & Meagher, 1990; Patterson, Cegavske, & to the stimulus relationships that underlie Pavlovian con- Thompson, 1973) are sensitive to environmental re- ditioning. We studied this phenomenon in Sprague – Daw- lationships. Spinal learning is observed in a variety ley rats by pairing a vibrotactile conditioned stimulus (CS) of species (Durkovic, 1975; Grau et al., 1990; Ince, with a tailshock unconditioned stimulus (US). Experiment Brucker, & Alba, 1978; Shurrager & Culler, 1940) 1 showed that spinal rats exhibit differential conditioning, and exhibits many of the basic characteristics identi- having longer tail-flick latencies on the tail-flick test dur- fied by Pavlov [e.g., extinction, differential condition- ing a CS that was paired with the US (conditioned antinoc- ing, overshadowing (Beggs et al., 1985; Grau et al., iception). Experiment 2 showed that rats trained with the 1990; Illich, Salinas, & Grau, 1994)]. cord intact still exhibit differential conditioning after the Research on spinal learning has been motivated cord is cut. This suggests that spinal learning contributes by two basic issues. First, neuroscientists would like to behavioral plasticity in intact subjects.  1997 Academic Press to develop model systems to study the biological mechanisms that underlie learning in vertebrates. Given that a great deal is known about spinal archi- Organisms learn about their world by encoding tecture (Price, 1988) and that spinal neurons can the spatial and temporal relationships that exist be- exhibit some interesting forms of plasticity (Coderre, tween environmental stimuli. This type of learning Katz, Vaccarino, Melzack, 1993; Leahy & Durkovic, can be studied in animals using the procedure of 1991; Wolpaw & Carp, 1990; Woolf & Thompson, Pavlov, in which a stimulus (the conditioned stimu- 1991), spinal learning may provide an attractive lus, or CS) is paired with a biologically meaningful model paradigm. Second, the study of spinal learn- event (the unconditioned stimulus, or US). As a re- ing should help to elucidate the relationship between sult of this experience, the paired CS (the CS / ) elicits learning and neural complexity. Presumably, the a response not observed to a CS presented in an forebrain enriches basic learning mechanisms in explicitly unpaired fashion (the CS 0 ). Pavlov be- some important ways. A comparison of the rules that lieved that this learning depended on the cerebral govern learning at different levels of the nervous cortex (Pavlov, 1927). However, subsequent studies system should facilitate the identification of proper- have demonstrated that lower level neural systems ties that are unique to higher level systems. in the brainstem (Bromily, 1948; Norman, Buch- To demonstrate spinal conditioning, researchers wald, & Villablanca, 1977) and the spinal cord have routinely transected the cord prior to training. (Beggs, Steinmetz, & Patterson, 1985; Durkovic, When learning is observed, it can be concluded that all of the mechanisms needed to encode the CS– 1 This research was supported by a grant from the National US relation must exist within the cord. However, Institute of Mental Health (MH48994) to J. W. Grau and M. W. isolating the cord in this fashion may do more than Meagher. The authors thank Tamara King for her help and ad- prevent supraspinal mediation; it may effectively re- vice. Reprint requests and correspondence concerning this article lease spinal systems from tonic inhibition, allowing should be addressed to Robin L. Joynes, Department of Psychol- them to exhibit forms of plasticity that would not ogy, Texas A&M University, College Station, TX 77843. E-mail: RLJ050A@ACS.TAMU.EDU. normally occur in intact subjects. 64 1074-7427/97 $25.00 Copyright  1997 by Academic Press All rights of reproduction in any form reserved.