Capacity for cortical excitation is reduced in psychotic disorders: An investigation of the TMS-EMG cortical silent period

We found evidence of reduced glutamatergic excitatory motor cortical capacity in three groups of patients with differing psychotic disorders.Exciting the motor pathway further through single pulse TMS stimulation did not create the increased motor evoked amplitude seen in the healthy control group.The course of illness in psychosis may be characterised by initial hyper-glutamatergic states, seen during the prodromal period and acute psychosis, followed by a relative hypo-glutamatergic state (Natsubori et al. 2014;de la Fuente-Sandoval et al. 2011).Our neurophysiological findings suggest that there is a reduction in excitatory capacity of inter-cortical excitatory connections of layer 5 pyramidal neurons with chronic psychotic illness: this reduction is indicative of long term depression (LTD), that is limited capacity to long term potentiation (LTP) which requires strong inter-cortical connectivity of pyramidal neurons.The behavioural implications of this finding are that individuals with persistent psychosis will find it difficult to learn new motor activities which require activation of the motor cortex, which supports the promotion of physical activity in patients with chronic psychotic illnesses, to promote inter-cortical connectivity of layer 5 pyramidal neurons.