Abnormal cortical synaptic plasticity in minimal hepatic encephalopathy

Area of Science:

• Neuroscience
• Clinical Neurology

Background:

• Minimal hepatic encephalopathy (MHE) is the earliest stage of hepatic encephalopathy (HE), characterized by subtle cognitive impairments without obvious clinical signs.
• Cognitive deficits in MHE affect attention, vigilance, and integrative functions.
• Motor cortex synaptic plasticity, particularly long-term potentiation (LTP)-like mechanisms, is implicated in motor learning.

Purpose of the Study:

• To investigate alterations in motor cortex synaptic plasticity in patients with MHE.
• To assess if MHE affects the ability to induce LTP-like effects in the motor cortex.

Main Methods:

• Utilized the paired associative stimulation (PAS) protocol with transcranial magnetic stimulation (TMS) to induce LTP-like effects.
• Recruited 15 MHE patients and 15 cirrhotic patients without MHE.
• Measured motor evoked potentials (MEPs) before and after PAS25 intervention (180 electrical stimuli of the median nerve paired with TMS over the abductor pollicis brevis hotspot at 25ms interstimulus interval).

Main Results:

• In healthy subjects, PAS25 significantly increased MEP amplitude, indicating successful induction of plasticity.
• In MHE patients, the PAS25 protocol resulted in a slight reduction of MEP amplitude.
• These results suggest impaired associative sensorimotor plasticity in MHE.

Conclusions:

• Associative sensorimotor plasticity, a measure of motor learning, is impaired in patients with minimal hepatic encephalopathy.
• The findings highlight a potential neurophysiological basis for motor deficits in the early stages of hepatic encephalopathy.