Interhemispheric plasticity is mediated by maximal potentiation of callosal inputs

Area of Science:

• Neuroscience
• Neuroplasticity
• Systems Neuroscience

Background:

• Unilateral injuries like stroke or amputation can lead to reorganization of brain functions.
• A key observation is the emergence of bilateral cortical activity in response to stimuli or movements from the unaffected body side.

Purpose of the Study:

• To elucidate the cellular and synaptic mechanisms driving interhemispheric cortical reorganization following unilateral sensory deprivation.
• To investigate how the brain adapts its functional connectivity after injury.

Main Methods:

• Utilized a mouse model of unilateral whisker deprivation.
• Employed functional magnetic resonance imaging (fMRI) to detect blood-oxygen-level-dependent responses in the somatosensory barrel cortex upon stimulation of intact whiskers.
• Conducted whole-cell electrophysiology to examine synaptic properties and neuronal excitability in the cortex.

Main Results:

• Stimulation of intact whiskers induced bilateral fMRI responses in the somatosensory cortex.
• The intact cortex demonstrated strengthened callosal synapses, particularly in layer 5 neurons projecting to the deprived hemisphere.
• These strengthened synapses exhibited enhanced AMPA and NMDA receptor-mediated responses, indicating maximal potentiation that occluded long-term potentiation (LTP).
• Changes in neuronal excitability and the excitation/inhibition balance were observed, consistent with cell-specific synaptic alterations.

Conclusions:

• The study demonstrates a cell-specific, synaptic mechanism underlying interhemispheric cortical reorganization after unilateral sensory loss.
• Strengthened callosal synapses play a critical role in adapting cortical function and connectivity.
• These findings offer insights into brain plasticity and potential therapeutic targets for recovery after neurological injury.