  Running title: Frontoparietal anodal tDCS reduces ketamine-induced
oscillopathies.Abstract: During the prodromal phase of schizophrenia with its
complex and insidious clinical picture, electroencephalographic recordings
detect widespread oscillation disturbances (or oscillopathies). Neural
oscillations are electro-biomarkers of the connectivity state within systems. A
single systemic administration of ketamine, a non-competitive NMDA glutamate
receptor antagonist, transiently reproduces the oscillopathies with a clinical
picture reminiscent of the psychosis prodrome. This acute pharmacological model
may help the research and development of innovative treatments against the
psychotic transition. Transcranial electrical stimulation is recognized as an
appropriate non-invasive therapeutic modality since it can increase cognitive
performance and modulate neural oscillations with little or no side effects.
Therefore, our objective was to set up, in the sedated adult rat, a stimulation
method able to normalize the ketamine-induced oscillopathies. Unilateral
transcranial frontoparietal anodal stimulation by direct current (<+1 mA) was
applied in ketamine-treated rats. A concomitant electroencephalographic
recording of the parietal cortex measured the stimulation effects on its
spontaneously-occurring oscillations. A 5-min bipolar anodal tDCS immediately
and quickly reduced, significantly with an intensity-effect relationship, the
ketamine-induced oscillopathies at least in the bilateral parietal cortex. A
duration effect was also recorded. These preliminary neurophysiological
findings are promising for developing a therapeutic proof-of-concept against
neuropsychiatric disorders.
