Thalamus Controls Development and Expression of Arousal States in Visual Cortex

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Systems Neuroscience

Background:

• Cerebral cortex development involves acquiring continuous spontaneous activity and state-dependent modulation.
• The underlying circuit mechanisms for these critical developmental milestones remain largely unknown.
• Understanding these mechanisms is crucial for assessing normal brain development and prognosis in vulnerable infants.

Purpose of the Study:

• To test the hypothesis that relay thalamus, not cortical circuitry, is the primary locus of circuit changes driving developmental acquisition of activity continuity and state dependence in sensory cortex.
• To investigate the role of the dorsal lateral geniculate nucleus (dLGN) in the development of visual cortex (VC) activity patterns.

Main Methods:

• Simultaneous electrophysiological recordings from the dLGN and VC in awake, head-fixed rats throughout early development.
• Utilized linear multielectrode arrays for precise localization of neural activity.
• Manipulated dLGN activity by silencing it after postnatal day 13 (P13) to assess its causal role.

Main Results:

• dLGN activity became continuous and positively correlated with movement (state dependence) on P13, coinciding with VC maturation and independent of VC activity.
• Silencing dLGN after P13 reversed developmental changes in VC, causing discontinuous activity and suppressing movement-related firing.
• Thalamic bursting, indicative of non-aroused states, emerged later on P16, suggesting developmental independence from earlier maturation processes.

Conclusions:

• Cellular or circuit changes within the relay thalamus are critical drivers for the maturation of background cortical activity.
• These thalamic changes precede and influence the development of cortical activity patterns, including continuity and state dependence.
• Findings provide insights into the circuit basis of human EEG maturation and its clinical relevance for preterm infants and those with brain injury.