Future work involves testing a further subject to confirm the modulation effects, and the systematic variation of the TMS SOA. Physiology Poster Only 118 Two phases of interhemispheric inhibition between motor related cortical areas and the primary motor cortex in human Ni Z, Gunraj C, Chen R, Toronto Western Hospital (Toronto, CA) Objective: Interhemispheric inhibition (IHI) refers to the neurophysiolog- ical mechanism in which one hemisphere of the brain inhibits the opposite hemisphere. Although IHI between bilateral motor cortices (M1s) has been extensively investigated, the IHI between other motor related cortical areas is still unclear. The purpose of the present study is to systematically explore IHI from different motor related cortical areas to the opposite M1. Method: We investigated IHI from five motor related areas in the right hemisphere to the left M1. These areas are hand and face representations of M1, dorsal premotor cortex (dPM), somatosensory cortex (S1) and dorso- lateral prefrontal cortex (DLPFC). Transcranial magnetic stimulation (TMS) using a conditioning-test paradigm was employed to study the IHIs. Test stimulation (TS) was delivered to the left M1. We used TS1mV as the TS intensity which is able to generate w1 mV motor evoked potentials (MEPs) in right first dorsal interosseous (FDI) muscle. Conditioning stimulation (CS) was delivered to one of five motor related areas in the right hemisphere. Three experiments were conducted. First, the time course of IHI was examined by testing different interstimulus intervals (ISIs). CS intensity used CS1mV (able to generate w1 mV MEPs in left FDI muscle). Second, the effects of different CS intensities were tested at ISIs of 10 and 50 ms. CS intensity was varied from 0.6 to 2.0 active motor threshold. Third, the effects of current directions of the CS were tested. We select medial, lateral, anterior and posterior as the CS current directions. CS1mV was the CS intensity. Result: Maximum IHI was found at ISIs of w10 ms (short interval IHI, SIHI) and w50 ms (long interval IHI, LIHI) for the motor related cortical areas tested. LIHI could be elicited over a wide range of CS intensities, whereas SIHI required higher CS intensities or was even absent from some areas. LIHI was produced by more CS current directions than SIHI. Conclusion: We conclude that there are two distinct phases of IHI from widely distributed motor related cortical areas to the opposite M1 through the corpus callosum, and they are mediated by different neuronal populations. Our finding suggests that widely distributed IHI may contribute to bilateral movements at different stages of motor control, including the decision making (DLPFC), movement selection (S1 and PMd) and execution (M1, PMd, S1) stages. rTMS Poster Only 119 High frequency rTMS applied to perilesional cortex ameliorates visuo-spatial deficits following focal posterior parietal damage Afifi L, Rushmore R, Japp B, Valero-Cabre A, Boston University School of Medicine (Boston, US) Objective: We used high frequency repetitive transcranial magnetic stimula- tion (rTMS) to increase the excitability of perilesional regions after chronic brain damage to promote functional restitution. We specifically targeted rTMS to a perilesional area previously determined to be an essential site of functional compensation after focal damage to the posterior parietal cortex. Methods: A group of adult cats (n 5 6) underwent extensive behavioral testing in a battery of tasks requiring visually guided orienting responses to static visual stimuli presented at eccentricities throughout the left and right visual hemifields. Once plateau performance levels were reached, an- imals received unilateral cortical lesions of the posterior visuo-parietal cor- tex, which resulted in impairments in the ability to detect and localize visual stimuli in the contralesional visual hemispace. Three months after lesion, all subjects underwent daily sessions of rTMS (10Hz rTMS, 2400 pulses at 40% intensity) for seventy sessions. Animals were evaluated daily after each session of rTMS and after every block of 5 sessions. Results: Following rTMS treatment, animals achieved either high, (n 5 4 subjects, 27 6 7%) moderate, (n 5 1 subjects, 17%) or no (n 5 1 subject, 0%) improvements in contralesional performance with respect to pre-TMS levels. Overall, recovery progressed from pericentral to peripheral targets with increasing rTMS sessions. A sham 10Hz TMS group (n 5 2) under- went an equivalent regimen and showed no changes in performance Conclusions: Our findings demonstrate that high frequency rTMS applied to perilesional cortical key areas is able to alleviate functional deficits in brain damaged subjects. These data have important implications for the use of rTMS to produce restitution in human patients afflicted by cerebral damage. Movement Disorders Poster Only 120 Are motor symptoms in CRPS type I caused by altered sensori- motor processing? Morgante F, Russo M, Naro A, Terranova C, Rizzo V, Risitano G, Girlanda P, Quartarone A, Universita ` di Messina (Messina, IT) Complex Regional Pain Syndrome (CRPS) is a painful disorder charac- terized by pain, edema and trophic changes of the skin. In CRPS type I no major nerve lesions are demonstrated. Although CRPS is mainly a sensory disorder, patients can also develop motor symptoms such as tremor, dystonia or fixed postures of a limb. Previous studies of functional neuroimaging have showed a reorganization of the motor areas in CRPS I along with alterations in the processing of sensory inputs. In the present study we evaluated with Transcranial Magnetic Stimulation (TMS), sensori-motor integration, corticospinal excitability and motor cortex plasticity in patients with Complex Regional Pain Syndrome (CRPS) type I, who have developed a fixed posture of the right hand. In 10 normal subjects and 10 patients with CRPS I (in the affected and in the non affected arm) we evaluated: intracortical inhibition (ICI) and facilitation (ICF); sensori-motor integration through short-latency (SAI) and long-latency (LAI) afferent inhibition; synaptic plasticity through paired associative stimulation (PAS). 276 Abstracts