Neural specializations for language: a developmental perspective

Sympathetic arousal as a marker of chronicity in childhood stuttering

PURPOSE

This study investigated whether sympathetic activity during a stressful speaking task was an early marker for stuttering chronicity.

METHOD

Participants were 9 children with persisting stuttering, 23 children who recovered, and 17 children who do not stutter. Participants performed a stress-inducing picture-naming task and skin conductance was measured across three time points.

RESULTS

Findings indicated that at the initial time point, children with persisting stuttering exhibited higher sympathetic arousal during the stressful speaking task than children whose stuttering recovered.

CONCLUSIONS

Findings are taken to suggest that sympathetic activity may be an early marker of heightened risk for chronic stuttering.

A theory of neurolinguistic development

This article offers a developmental theory of language and the neural systems that lead to and subserve linguistic capabilities. Early perceptual experience and discontinuities in linguistic development suggest that language develops in four phases that occur in a fixed, interdependent sequence. In each phase of language, a unique ontogenetic function is accomplished. These functions have proprietary neural systems that vary in their degree of specialization. Of particular interest is an analytical mechanism that is responsible for linguistic grammar. This mechanism is time-locked and can only be turned on in the third phase. Confirming evidence is provided by children who are delayed in the second phase of the language learning process. These children store insufficient lexical material to activate their analytic mechanism. Inactivation behaves like damage, shifting language functions to homologous mechanisms in the nondominant hemisphere, thereby increasing functional and anatomical symmetry across the hemispheres. This atypical assembly of neurolinguistic resources produces functional but imperfect command of spoken language and may complicate learning of written language. The theory thus offers a different role for genetics and early experience, and a different interpretation of neuroanatomic findings, from those entertained in most other proposals on developmental language disorders.

Gradual emergence of developmental language disorders

This article presents a theory of normal and delayed development of language. According to the theory, linguistic capacity develops in critically timed phases that occur gradually and sequentially. Normally, the rapid accumulation of stored utterances activates analytical mechanisms that are needed for the development of linguistic grammar. Children with slowly developing brains have delays in the socially cognitive systems that store utterances, and a critical period for activation of experience-dependent grammatical mechanisms declines without optimal result. Continuing efforts to speak induct species-atypical allocations of neural resources into linguistic service. It is speculated that this compensatory activity leads to compensatory growth, which may ultimately be revealed as volumetric symmetry of perisylvian areas. Because rate of brain maturation is under genetic as well as environmental control, the stage is thus set for an impairment that will seem to be specific and a brain that will appear to be abnormal.