Commentary: "Compensatory plasticity: time matters".

摘要: The mammalian nervous system can adapt to the challenges of life through neural plasticity. brain will undergo extensive reorganization following sensory deprivation or damage afferent pathways (Kaas, 2001). This plastic develops as a function time. A recent review on plasticity in blind (Lazzouni and Lepore, 2014) stressed importance critical periods influence duration re-organization cortices. Such considerations are paralleled hearing sciences, sharing authors' opinion that “time matters.” Restoring lost deaf cortex, via surgically implanted devices offers unique insight into reorganization, allowing scientists follow transition from hearing, sighted. While retinal implants just becoming available clinical setting (Zrenner et al., 2010), cochlear (CIs) have been offered since 1980s (Clark, 2003). Here we argue that, for auditory implants, time matters along two dimensions: pre post-implantation. On one hand, is especially strong when occurs at early stages development. Referred sensitive period development, it provides cut-off ages guide implantation (Sharma 2002; Bedny 2010). other functional maturity cortex crucially depends experience (Kral 2005), emphasizing rehabilitation. Age plays substantial role performance with CI. Research has shown existence an development demonstrated how deprivation-driven changes affected by age. Cats were after fifth month age had smaller activation areas compared cats earlier, even they longer implant 2002, 2005; Kral Sharma, 2012). In humans, latency morphology P1 component auditory-evoked potentials serve biomarker central 2005b; Dorman 2007; O'Donoghue, Using this measure, optimal cortical was identified. Children before 3.5 years showed faster more robust than children past seven. Sharma al. (2002) observed 55 out 57 early-implanted latencies within range age-matched normal-hearing vs. 10 29 middle-implanted 1 21 late-implanted children, despite all being matched use duration. In longitudinal study, atypical morphologies during first year whereas group rapid 2005a). Behavioral studies also show better language 3 (Nikolopoulos 1999; Kirk 2002), which correlates well (Lee 2001; Giraud 2002). Thus, both animal human CI suggest stronger implant. Despite dominant implantation, induces system—at peripheral level—stressing post-implantation rehabilitation (Sandmann 2009). Spiral ganglion neurons play relaying information; deafened guinea pigs electrical stimulation prevented their retrograde degeneration increased size (Shepherd 1983, 1994; Losteau, 1987; Leake 1991, Li 1999). Similarly, CIs restorative effect medial superior olive, key brainstem structure (Tirko Ryugo, 2012). resulted improvements. Activation primary secondary regions response sound patients week switch-on (Giraud 2001); increased, authors consistently reduction number activated clusters regions, indicating tuning region. individuals, illustrating complex interaction between factors 2002). Returning parallel visual deprivation, still not possible currently only adults. However, several questions arise, instance, observe similar benefit implanting implants? As aid positive outcomes (Lazard 2012), substitution hinder restoration? par Lazzouni Lepore's 2014), research supports compensatory adaptation theory, whereby deafferentiated reorganizes adapts loss. Anatomical take place auditory-deprived brain, contrary general loss hypothesis would predict undifferentiated degradation function. Moreover, different perspective theory. Whether detrimental beneficial very much open debate (see Heimler 2014 review). Cross-modal limit instance Sandmann but cases, enhance (Mitchell Maslin, Rouger 2007). Time spent deprived state may solving apparent contradiction Lee, Lee How soon too surgical maximize risk-benefit trade off debated highly individual (James Papsin, 2004; Colletti 2012; Hagr 2015). In sum, acquiring experiences matter cope change. Stimulating impaired sense restoring shall benefits implantation.