Specificity of human parietal saccade and reach regions during transcranial magnetic stimulation

• Published in: The Journal of neuroscience 2010-09, Vol.30 (39), p.13053-13065
• Main Authors: Vesia, Michael, Prime, Steven L, Yan, Xiaogang, Sergio, Lauren E, Crawford, J Douglas
• Format: Article
• Language: English
• Subjects: Adult; Brain Mapping - methods; Executive Function - physiology; Female; Functional Laterality - physiology; Humans; Macaca; Male; Movement - physiology; Neuropsychological Tests; Parietal Lobe - anatomy & histology; Parietal Lobe - physiology; Photic Stimulation - methods; Psychomotor Performance - physiology; Saccades - physiology; Task Performance and Analysis; Transcranial Magnetic Stimulation - methods; Volition - physiology; Young Adult
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.1644-10.2010

Single-unit recordings in macaque monkeys have identified effector-specific regions in posterior parietal cortex (PPC), but functional neuroimaging in the human has yielded controversial results. Here we used on-line repetitive transcranial magnetic stimulation (rTMS) to determine saccade and reach specificity in human PPC. A short train of three TMS pulses (separated by an interval of 100 ms) was delivered to superior parieto-occipital cortex (SPOC), a region over the midposterior intraparietal sulcus (mIPS), and a site close to caudal IPS situated over the angular gyrus (AG) during a brief memory interval while subjects planned either a saccade or reach with the left or right hand. Behavioral measures then were compared to controls without rTMS. Stimulation of mIPS and AG produced similar patterns: increased end-point variability for reaches and decreased saccade accuracy for contralateral targets. In contrast, stimulation of SPOC deviated reach end points toward visual fixation and had no effect on saccades. Contralateral-limb specificity was highest for AG and lowest for SPOC. Visual feedback of the hand negated rTMS-induced disruptions of the reach plan for mIPS and AG, but not SPOC. These results suggest that human SPOC is specialized for encoding retinally peripheral reach goals, whereas more anterior-lateral regions (mIPS and AG) along the IPS possess overlapping maps for saccade and reach planning and are more closely involved in motor details (i.e., planning the reach vector for a specific hand). This work provides the first causal evidence for functional specificity of these parietal regions in healthy humans.