Role of Prefrontal Cortex in Learning and Generalizing Hierarchical Rules in 8-Month-Old Infants

Abstract

Recent research indicates that adults and infants spontaneously create and generalize hierarchical rule sets during incidental learning. Computational models and empirical data suggest that, in adults, this process is supported by circuits linking prefrontal cortex (PFC) with striatum and their modulation by dopamine, but the neural circuits supporting this form of learning in infants are largely unknown. We used near-infrared spectroscopy to record PFC activity in 8-month-old human infants during a simple audiovisual hierarchical-rulelearning task. Behavioral results confirmed that infants adopted hierarchical rule sets to learn and generalize spoken object-label mappings across different speaker contexts. Infants had increased activity over right dorsal lateral PFC when rule sets switched from one trial to the next, a neural marker related to updating rule sets into working memory in the adult literature. Infants' eye blink rate, a possible physiological correlate of striatal dopamine activity, also increased when rule sets switched from one trial to the next. Moreover, the increase in right dorsolateral PFC activity in conjunction with eye blink rate also predicted infants' generalization ability, providing exploratory evidence for frontostriatal involvement during learning. These findings provide evidence that PFC is involved in rudimentary hierarchical rule learning in 8-month-old infants, an ability that was previously thought to emerge later in life in concert with PFC maturation.

A novel ecological account of prefrontal cortex functional development.

“…Similarly, short direct projections between anterior temporal lobe and PFC that support auditory processing and speech perception (Romanski & Goldman-Rakic, 2002; Scott & Johnsrude, 2003) may also specialize relatively early to support language development. This prediction aligns with evidence showing increased PFC activation in infants when hearing infant-directed but not adult-directed speech (Saito et al, 2007), forward but not backward speech (Dehaene-Lambertz et al, 2002), and when organizing words by hierarchical contexts (Werchan et al, 2016). Other areas within the frontal lobe, such as the premotor area, may begin to specialize for control over more complex motor actions soon thereafter.…”

“…Additional results suggested that infants also used this learning mechanism to help structure different spoken labels for the same objects into hierarchical rule structures, akin to learning in a bilingual environment. Recent work using NIRS provided evidence that this learning mechanism is related to right dlPFC activation in 8-month-old infants (Werchan et al, 2016). Taken together, this body of evidence suggests the possibility that PFC, and dlPFC in this example, may be involved in creating rule structures that help organize linguistic, social, emotional, and oculomotor learning and action as early as in infancy.…”

“…This redefinition offers the prediction that developmental continuity should be observed in PFC’s computations when ecologically appropriate tasks are used at different developmental stages. For example, the PFC is involved in hierarchically organizing and processing language in infancy, recalling the data on infant-directed speech (Saito et al, 2007) and hierarchical learning of languages in context (Werchan et al, 2016). Early language development has been shown to be a strong predictor of later, more classic frontostriatal executive functions tasks in childhood (e.g., (Gooch, Thompson, Nash, Snowling, & Hulme, 2016; Kuhn, Willoughby, Vernon-Feagans, & Blair, 2016; Noble, McCandliss, & Farah, 2007; Noble, Norman, & Farah, 2005).…”

The relationship between cognitive enrichment and cognitive control: A systematic investigation of environmental influences on development through socioeconomic status

“…Mechanistically, the formation of stable rule representations for action arises from frontostriatal reinforcement learning mechanisms during childhood (Snyder & Munakata, ; Werchan, Collins, Frank, & Amso, , ). Computational models of the formation of these representations have emphasized the variability of experience as key determining factors.…”

Actions speak louder than words: Differences in memory flexibility between monolingual and bilingual 18‐month‐olds

“…Hierarchical learning is associated with the frontostriatal pathway and some research has examined this in infants. For example, activation of the right dorsal lateral prefrontal cortex is associated with better memory generalization performance in monolingual infants (Werchan, Collins, Frank, & Amso, ). Further, infants’ eye blink rate, a possible physiological index of striatal dopamine activity, was positively associated with generalization performance.…”