Developmental progression of thalamic and cortical sensory networks in mice

Resumo

A key question that remains unclear in Developmental Neuroscience is to understand how thalamic spontaneous activity contributes to the emergence and plasticity of cortical sensory maps. Spontaneous neural activity during development plays an important role in the establishment of thalamocortical circuitry in sensory areas before sensory onset. It is thought that the cortical activity at perinatal stages strengthens synaptic connections that will define sensory maps. Spontaneous activity in the developing cortex has been well characterized: it starts as highly correlated patches of active neurons that, after the first postnatal week in mice, switches to a sparser and decorrelated neuronal firing that allows an efficient neuronal coding. By contrast, the profile and function of spontaneous activity in the developing thalamus remains largely unknown. Here, we described the maturation of the spontaneous spiking activity in the thalamic nuclei of mice aged from postnatal day 6 to 14. The overexpression of Kir2.1 in the developing thalamus not only alters this maturation but also affects the electrical activity in the corresponding sensory cortices. We have also observed this link between the maturation of the thalamic and cortical stations in models of early sensory deprivation. When visual input is removed embryonically, the visual and somatosensory thalamus and cortex exhibit abnormal patterns of spontaneous activity at immature stages. In the visually deprived pups, neurons from the primary somatosensory cortex respond faster upon whisker stimulation, a fact that might underlie more efficient information processing in the intact sensory modalities. Our results evidence that normal thalamic activity during development is crucial for the correct organization of cortical circuits and for cross-modal changes both in thalamus and cortex after sensory deprivation.