Left hemispheric breakdown of LTP-like cortico-cortical plasticity in schizophrenic patients.

Objective: Altered cortical connectivity and plasticity seems to be asymmetrical between the hemispheres in patients with schizophrenia (SCZ). We evaluated long-term potentiation (LTP) in parietal-frontal circuits of both hemispheres using a cortico-cortical Paired Associative Stimulation (cc-PAS) protocol testing the rules of Hebbian-like spike timing dependent plasticity (SPTD).

Methods: 12 SCZ and 12 healthy subjects (HS) underwent a cc-PAS protocol to activate, by means of paired pulses of transcranial magnetic stimulation (TMS), the short-latency connection between posterior parietal cortex (PPC) and primary motor cortex (M1) of both hemispheres. Motor-evoked potentials (MEPs) were collected to assess the time course of the after effects of cc-PAS protocol measuring MEP amplitude as index of cortico-cortical associative plasticity.

Results: While HS showed a similar time course of LTP-like plasticity in the two hemispheres, SCZ revealed a weaker late-LTP-like plasticity in the left compared to the right hemisphere after cc-PAS protocol.

Conclusions: SCZ failed to show the typical long-lasting increase of M1 excitability observed after cc-PAS protocol in both hemispheres, with a greater reduction in the left one.

Significance: Our findings provide novel neurophysiological evidence for an asymmetric impairment of the left parietal-frontal network in SCZ patients.