Facilitation of Fast Backward Priming After Left Cerebellar Continuous Theta-Burst Stimulation

Abstract

Traditional theories of backward priming account only for the priming effects found at long stimulus onset asynchronies (SOAs). Here, we suggest that the presence of backward priming at short SOAs may be related to the integrative role of the cerebellum. Previous research has shown that the right cerebellum is involved in forward associative priming. Functional magnetic resonance imaging reveals some activation of the left cerebellar hemisphere during backward priming; but what this activation represents is unclear. Here we explore this issue using continuous theta-burst transcranial magnetic stimulation (cTBS) and associative priming in a lexical decision task. We tested the hypothesis that the left cerebellum plays a role in backward priming and that this is dissociated from the role of the right cerebellum in forward priming. Before and after cTBS was applied to their left and right cerebellar hemispheres, participants completed a lexical decision task. Although we did not replicate the forward priming effect reported in the literature, we did find a significant increase in backward priming after left relative to right cerebellar cTBS. We consider how theories of cerebellar function in the motor domain can be extended to language and cognitive models of backward priming.

An Opponent Process Cerebellar Asymmetry for Regulating Word Association Priming

“…stimulus onset asynchronies (SOAs) between prime and target words > 600 ms), this pattern will not be present and, indeed, based on the effects of right cerebellar TMS in the Visual World Paradigm, would actually be expected to be the reverse: a decrease in word association priming after left and an increase word association priming after right cerebellar theta-burst stimulation. While this specific prediction has not yet been tested explicitly, it is interesting to note that the only other study of word association priming in which the left cerebral hemisphere was stimulated reported, in contrast with our findings, an increase in priming [ 19 ]. That experiment, like ours, employed a short interval (250 ms) between prime and target word.…”

“…That experiment, like ours, employed a short interval (250 ms) between prime and target word. However, Allen-Walker et al [ 19 ] examined backward priming in which the prime word was associated with the target word, but did not predict it. For example, in the pair dog-BONE, dog is predictive of bone; whereas the two words are much less likely to appear in the reverse order bone followed by dog.…”

“…For example, in the pair dog-BONE, dog is predictive of bone; whereas the two words are much less likely to appear in the reverse order bone followed by dog. In this latter case of backward priming, the lexical decision on the target word can be aided by retrieving the prime word from episodic memory or as Allen-Walker et al [ 19 ] suggested by a feedback loop. Such post lexical processing can begin only after the meanings of both prime and target words have been successfully extracted.…”

“…Building on studies of ataxic dysarthria (a disruption of speech articulation and prosody), Ackermann [ 15 ] has specified a role for the cerebellum in the ‘temporal organisation’ of speech, an argument that has been expanded upon by Kotz and Schwartze [ 16 ]. While some authors do support a role for the cerebellum in temporal and spatial sequencing of activities [ 17 ], others give more weight to its function as a comparator of temporally accurate predictions or internal models [ 18 ] with the actual sensory feedback of action (reafference) [ 19 ]. It has, however, been pointed out that all predictions contain a ‘what’ and a ‘when’ element (to some degree).…”

“…We could identify only two TMS language studies that have included left cerebellar stimulation. Allen-Walker and coworkers [ 19 ] found evidence of left cerebellar involvement in backward priming at short intervals, whereas Runnqvist and colleagues [ 23 ] found no evidence for left cerebellar involvement in a speech production task. Elsewhere, a study that imaged metabolic changes before and after TMS of the left cerebellum (1 cm below inion and 3 cm lateral) noted changes bilaterally in the superior and middle temporal gyri [ 24 ].…”