Spike timing and synaptic dynamics at the awake thalamocortical synapse

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Sensory Processing

Background:

• Thalamocortical (TC) neurons heavily influence cortical layer 4 despite low synapse numbers.
• TC synapses exhibit high efficacy but also activity-dependent depression.
• In vivo spontaneous activity in awake animals may lead to chronic synaptic depression.

Purpose of the Study:

• Investigate the relationship between TC spike timing and synaptic efficacy in awake rabbits.
• Examine TC synaptic function during thalamic relay and burst modes.
• Understand how spontaneous activity impacts TC synaptic strength in the somatosensory system.

Main Methods:

• Cross-correlation analysis of single TC neuron impact on layer 4 interneurons.
• Spike-triggered extracellular field potentials and current source-density analysis in cortical barrel columns.
• Examination of synaptic currents and field potentials in response to TC impulses with varying interspike intervals (ISIs).

Main Results:

• TC bursts and isolated spikes with long ISIs more effectively elicited postsynaptic action potentials.
• Synaptic currents in layers 4 and 6 were greatly enhanced by TC impulses with long preceding ISIs.
• Chronic depression at awake TC synapses is relieved by long ISIs, particularly preceding bursts.

Conclusions:

• Long ISIs, characteristic of TC bursts, powerfully activate cortical circuits by overcoming chronic synaptic depression.
• Spontaneous activity patterns significantly modulate TC synaptic efficacy in vivo.
• Understanding TC synaptic dynamics is crucial for comprehending sensory information processing in the cortex.