One (1) defining characteristic of learning deficits associated with developmental disabilities is difficulty learning conditional or semantic relations among stimuli that do not share common physical features. One (1) such example is learning that the word """"""""TWO"""""""" and the number """"""""2"""""""" are semantically related or that """"""""TWO"""""""" """"""""2"""""""" and """"""""OO"""""""" (2 circles) may be members of the same concept. The present R03 small grant proposal is designed to reveal the functional neuroanatomy of a process known as stimulus equivalence. Stimulus equivalence (SE) is a process by which reinforcement contingencies are manipulated during direct training to establish a set of learned conditional/semantic relations among stimuli, for example, learning the conditional relation if stimulus A, select stimulus B (A:B), and a second conditional relation, B:C. During subsequent testing, several new relations have been found to """"""""emerge"""""""" without direct training. These SE relations are termed: symmetry (B:A), transitivity (A:C), and equivalence (C:A). To broaden our understanding of the neuroanatomy of conditional/semantic learning deficits in developmental disabilities, we investigated SE processes in healthy adults using fMRI. Results showed SE relations produced frontal-striatal activation in regions implicated in reward processing and decision making. In this proposal, we will use BOLD fMRI to demonstrate that discriminations of SE relations involve the striatum and ventral frontal cortex. We will also investigate frontal-striatal responses to SE relations established through different consequences (nonverbal vs. verbal) and different mechanisms (contingencies vs. instructions). Results obtained with healthy adult subjects will help us to further test and develop our model of frontal-striatal involvement in SE.
