Imaging human intra-cerebral connectivity by PET during TMS

Abstract

Non-invasive imaging of human inter-regional neural connectivity by positron emission tomography (PET) during transcranial magnetic stimulation (TMS) was performed. The hand area of primary motor cortex (M1) in the left cerebral hemisphere was stimulated with TMS while local and remote effects were recorded with PET. At the stimulated site, TMS increased blood flow (12-20%) in a highly focal manner, without an inhibitory surround. Remote covariances, an index of connectivity with M1, were also focal. Connectivity patterns established in non-human species were generally confirmed. Excitatory connectivity (positive covariance) was observed in ipsilateral primary and secondary somatosensory areas (S1 and S2), in ipsilateral ventral, lateral premotor cortex (M2) and in contralateral supplementary motor area (SMA). Inhibitory connectivity (negative covariance) was observed in contralateral M1.

Electrical Stimulation of Rat Medial Prefrontal Cortex Enhances Forebrain Serotonin Output Implications for Electroconvulsive Therapy and Transcranial Magnetic Stimulation in Depression

“…In recent years, repetitive TMS of the left dorsolateral prefrontal cortex has emerged as a successful antidepressant treatment (Pascual-Leone et al 1996;George et al 1997). Although the exact mechanism underlying the efficacy of TMS is still unclear, this stimulation procedure probably induces focal activation of PFC neurons, as revealed by simultaneous measurements of cerebral glucose metabolism and blood flow (George et al 1995;Paus et al 1997;Fox et al 1997).…”

“…In recent years, repetitive TMS of the left dorsolateral prefrontal cortex has emerged as a successful antidepressant treatment (Pascual-Leone et al 1996;George et al 1997). Although the exact mechanism underlying the efficacy of TMS is still unclear, this stimulation procedure probably induces focal activation of PFC neurons, as revealed by simultaneous measurements of cerebral glucose metabolism and blood flow (George et al 1995;Paus et al 1997;Fox et al 1997).Apart from decreased PFC activity, a functional deficiency in serotonergic neurotransmission is considered as another characteristic feature of depression (Maes and Meltzer 1995). The therapeutic efficacy of various antidepressant treatments is thought to result from their ability to enhance serotonergic function (Blier and De Montigny 1994).…”

Transcranial magnetic stimulation: studying the brain--behaviour relationship by induction of ‘virtual lesions’

“…In this case, fMRI and PET studies could evaluate the functional adaptation of brain activity to the modulation of neural activity in an element of a neural network whose activity has been previously demonstrated to be associated with a given behaviour (Pascual-Leone et al 1998). Finally, instead of using a cognitive task, TMS can provide a controlled stimulation of a speci¢c region of the subject's brain (Fox et al 1997;Ilmoniemi et al 1997;Paus et al 1997;Bohning et al 1999). In this case, concurrent measures of regional blood-£ow or EEG during and following TMS could be used to assess functional brain connectivity independently of the subject's behavioural state.…”

“…Nevertheless, this limitation does not extend to the degree that one cannot claim preferential e¡ects on a given brain structure or rule out direct extension of the TMS e¡ects to distant cortical areas. It is probable that the e¡ects of TMS (particularly of rTMS) might spread along neural connections to a¡ect distant cortical and subcortical structures (Fox et al 1997;Ilmoniemi et al 1997;Paus et al 1997;Pascual-Leone et al 1998;Bohning et al 1999). Nevertheless, direct TMS e¡ects to a given cortical target appear to be limited to a de¢nable tissue volume.…”

A primer on the treatment of schizophrenia through repetitive transcranial magnetic stimulation

“…Given the excitatory effects of high frequency rTMS (5-20 Hz) [25], several studies have explored targeting the dorsolateral prefrontal cortex (DLPFC) to reduce negative symptoms. The common hypothesis has been that high-frequency rTMS would decrease negative schizophrenia symptoms by modulating perfusion, cerebral metabolism and neuronal excitability in the prefrontal cortex [26][27][28]. A statistically significant, albeit small, clinical decrease in negative symptom intensity was reported by Cohen et al in a study of six subjects [29].…”