Selective Strengthening of Intracortical Excitatory Input Leads to Receptive Field Refinement during Auditory...

Area of Science:

• Neuroscience
• Auditory System Development
• Sensory Cortex Plasticity

Background:

• Postnatal development refines sensory cortex function, reducing receptive field size.
• In rat primary auditory cortex (A1), layer 4 (L4) neuron excitatory input refinement sharpens frequency selectivity.
• The specific contributions of thalamocortical and intracortical inputs to this sharpening are not fully understood.

Purpose of the Study:

• To investigate developmental changes in excitatory inputs to A1 L4 neurons.
• To determine how thalamocortical and intracortical circuits contribute to frequency tuning refinement.
• To elucidate the mechanisms underlying sharpening of excitatory input tuning in A1 L4 neurons.

Main Methods:

• In vivo whole-cell recordings in young rats (both sexes).
• Pharmacological silencing of cortical spiking to isolate input pathways.
• Analysis of auditory thalamic neuron output, thalamocortical input, and intracortical excitatory input to A1 L4 neurons.
• Computational modeling to assess the role of recurrent connections.

Main Results:

• Auditory thalamic maps matured, but output tuning remained unchanged.
• Both thalamocortical and intracortical excitatory inputs to A1 L4 neurons showed sharpened tuning.
• Intracortical input exhibited better tuning than thalamocortical input, with selective strengthening around the optimal frequency.
• Modeling confirmed that frequency-selective strengthening of local recurrent excitatory connections is crucial for tuning refinement.

Conclusions:

• Developmental refinement of excitatory input tuning in A1 L4 neurons occurs at both thalamocortical and intracortical levels.
• Thalamic output tuning does not change during this refinement period.
• Strengthened intracortical excitation plays a dominant role in refining the frequency selectivity of A1 L4 neurons.