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Areas around the horizontal part of the intraparietal sulcus (hIPS) have repeatedly been reported to participate in processing numerical magnitude. Using transcranial magnetic stimulation (TMS), we investigated the functional role of the hIPS by examining two effects from the domain of numerical cognition: in magnitude comparison tasks response latencies are inversely related to the numerical distance between two numbers. This distance effect indexes access to the mental number representation. In magnitude comparison tasks responses are faster when decade and unit comparison would lead to the same decision (e.g. 42&#95;57, 4 < 5 and 2 < 7) than when they would not (e.g. 47&#95;62, 4 < 6 but 7 > 2). This compatibility effect reflects unit-decade integration processes. Differential susceptibility of (fe)male participants to TMS was examined. We applied repetitive TMS (rTMS; 1Hz for 10 min) over the left hIPS in 12 participants (6 female). No stimulation and vertex stimulation served as control conditions. The effect of rTMS was mediated by gender: in male participants, the distance effect decreased after TMS over hIPS. For female participants distance and compatibility effect both increased. This modulation of the compatibility effect was limited in duration to no more than 4 min. The hIPS seems to be functionally involved both in number magnitude processing and in integrating unit-decade magnitude information of two-digit numbers. Relative hemispheric specialization of the hIPS with respect to two-digit magnitude comparison is discussed.

Objective: Phantom pain is linked to a reorganization of the partially deafferented sensory cortex. In this study we have investigated whether the pain syndrome can be influenced by repetitive transcranial magnetic stimulation (rTMS)., Methods: Two patients with a longstanding unilateral avulsion of the lower cervical roots and chronic pain in the arm were studied. As a control the acute effects of rTMS (15 Hz, 2 s duration) on pain were studied in 4 healthy subjects. Pain intensity was assessed with the Visual Analogue Scale., Results: Stimulation of the contralateral parietal cortex led to a reproducible reduction in pain intensity lasting up to 10 min. Stimulation of other cortical areas produced only minor alterations in the severity of the pain. Both 1 and 10 Hz rTMS trains applied to the contralateral parietal cortex on weekdays for 3 consecutive weeks did, however, not lead to permanent changes in the pain intensity. Experimentally induced pain (cold water immersion of the right hand) in normal subjects was not influenced by rTMS., Conclusions: These results do not favor the use of rTMS in the treatment of phantom limb pain. The results, however, support the concept that phantom pain is due to a dysfunctional activity in the parietal cortex. The transient rTMS-induced analgesic effect may be due to a temporary interference with the cerebral representation of the deafferented limb.

The human posterior parietal cortex (PPC) is well known to be involved in various functions of multisensory spatial perception. However, the specific role of the PPC in hearing has, up to now, remained unclear. To allow more reliable conclusions to be drawn on this issue, we have used repetitive transcranial magnetic stimulation in healthy subjects. Focal stimulation of the PPC induced a systematic shift in the lateralization of interaural time differences (ITDs, a main cue for auditory azimuth), whereas the acuity of ITD discrimination was unaffected. We propose that the PPC is specifically involved in relating azimuthal angles of sound to the body coordinates and is part of a "where" stream in cortical processing of auditory information.