Abstract
Language acquisition in humans and song learning in songbirds naturally happen as a social learning experience, providing an excellent opportunity to reveal social motivation and reward mechanisms that boost sensorimotor learning. Our knowledge about the molecules and circuits that control these social mechanisms for vocal learning and language is limited. Here we propose a hypothesis of a role for oxytocin (OT) in the social motivation and evolution of vocal learning and language. Building upon existing evidence, we suggest specific neural pathways and mechanisms through which OT might modulate vocal learning circuits in specific developmental stages.
Highlights
Language acquisition in humans and song learning in songbirds naturally happen as a social learning experience, providing an excellent opportunity to reveal social motivation and reward mechanisms that boost sensorimotor learning
This experiment was made for secondlanguage learning, leaving unanswered the question of whether the primary speech learning mechanisms can be dissociated from the relevant motivational and rewarding mechanisms provided by social interactions
We suggest that OT has a role in social motivation of auditory and vocal communication behaviours in vocal non-learners, and that a lateralized function in the auditory cortex may have been present before vocal learning and language evolved
Summary
Oxytocin, depending on the brain region and release site, acts as a hormone, neuromodulator or neurotransmitter that functions through its receptor (OTR) to regulate a diverse set of biological processes: pregnancy and uterine contractions, milk ejection, attachment between mothers and their young, bond formation, copulation and orgasm, suppression of stress, thermoregulation, olfactory processing, eye contact and recognition of familiar individuals [25], with the caveat that some functions are specific to one lineage, such as mammals. Follow-up studies showed that OTR levels are remarkably lateralized with higher expression in neurons of the left auditory cortex [26] These observations in vocal non-learners strike us as relevant, as auditory and vocal learning/language circuits in humans are mainly leftlateralized [38], and are either left- or right-lateralized among different species of song-learning birds [39]. The analogous anterior pathway has been proposed to be a cortical-basal ganglia-thalamo-pallial loop involving Broca’s area (LMAN analogue), part of the anterior striatum (ASt) and the anterior thalamus; the analogous human posterior pathway has been proposed to include the laryngeal motor cortex (LMC; figure 1a), with different cortical layers representing songbird HVC (layer 3) and RA (layer 5) [2,16] This forebrain vocal pathway is either absent or limited at best in vocal non-learning species, including non-human primates and mice [54,55]. We propose a testable mechanism, either via direct influence on vocal learning pathways or indirect through the VTA DA neuron pathway
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