Brain correlates of language learning: the neuronal dissociation of rule-based versus similarity-based learning

Abstract

Language learning is one of the mysteries of human cognition. One of the crucial questions is the following: Does acquisition of grammatical knowledge depend primarily on abstract rules or on item-specific information? Although there is evidence that both mechanisms contribute to language acquisition, their relative importance during the process of language learning is unknown. Using an artificial grammar paradigm, we show by means of functional magnetic resonance imaging that the brain dissociates the two mechanisms: the left anterior hippocampus supports similarity-based learning, whereas the left ventral premotor cortex is selectively engaged by abstract rule processing. Moreover, data analysis over time on learning suggests that similarity-based learning plays a nonobligatory role during the initial phase, and that rule-based abstraction plays a crucial role during later learning.

Figures

Figure 1.

Schematic representation of the artificial grammar of BROCANTO. Nodes in the top panel specify word classes (nouns, verbs, etc.), whereas arrows denote valid transitions between nodes. A correct sentence is formed by a transition from beginning ([) to end (]). The bottom panel depicts the rules according to which valid phrases are formed. Thus, a sentence (S) consists of a noun phrase (NP) and a verb phrase (VP). A NP in turn is either the sequence dN or DMN, where N is one of the possible noun choices. Word categories: N, noun; v, verb; M, adjective; m, adverb; d, determiner in NP; D, determiner in modified NP (i.e., NP with adjective).

Figure 2.

Performance (with SE bars) across participants of the RULE and WORD condition. The beginning of changes is indicated by an arrow. Note that a change of abstract rules resulted in a significant decrease in the performance of grammaticality judgments immediately after the change and during subsequent learning of the new rule.

Figure 3.

Brain regions in which a significant condition-by-time interaction was observed. The sagittal sections at x = -26 mm (left panel) and x = -48 mm exhibit brain areas with changes of activity during learning relative to recurring control. Decreased activity in the left anterior hippocampus was noted for similarity-based learning only (top left panel, indicated by arrow). Regions demonstrating increased activity during learning included the left ventral premotor cortex and was predominant for rule-based learning (top right panel). Time courses of brain activity in the hippocampus (bottom left) and the premotor cortex (bottom right) illustrate this differential effect.