Covert Speech Arrest Induced by rTMS over Both Motor and Nonmotor Left Hemisphere Frontal Sites

Blocking the capacity to speak aloud (overt speech arrest, SA) may be induced by repetitive transcranial magnetic stimulation (rTMS). The possibility, however, of blocking internal speech (covert SA) has not been explored. To investigate this issue, we conducted two rTMS experiments. In the first experiment, we stimulated two left frontal lobe sites. The first was a motor site (left posterior site) and the second was a nonmotor site located in correspondence to the posterior part of the inferior frontal gyrus (IFG) (left anterior site). The corresponding right hemisphere nonmotor SA site was stimulated as a control. In the second experiment, we focused on the right hemisphere and stimulated a right hemisphere motor site (right posterior site), and, as control sites, a right hemisphere nonmotor site corresponding to the IFG (right anterior site) and a left hemisphere anteromedial site (left control). For both experiments, participants performed a syllable counting task both covertly and overtly for each stimulation site. Longer latencies in this task imply the occurrence of an overt and/or covert SA. All participants showed significantly longer latencies when stimulation was either over the left posterior or the left anterior site, as compared with the right hemisphere site (Experiment 1). This result was observed for the overt and covert speech task alike. During stimulation of the posterior right hemisphere site, a dissociation for overt and covert speech was observed. An overt SA was observed but there was no evidence for a covert SA (Experiment 2). Taken together, the results show that rTMS can induce a covert SA when applied to areas over the brain that are pertinent to language. Furthermore, both the left posterior/motor site and the left anterior/IFG site appear to be essential to language elaboration even when motor output is not required.

Variation of Soutellar Bristles in Drosophila

Three strains (70, 71, and 73) of D. melanogaster, wild type for the scute locus, were exposed to temperatures of 16, 20, 25, and 30�0 during larval development. They were found to vary in their temperature response; strain 70 showed a maximum development of additional bristles at the anterior site at l6�C, additional bristles were most frequent at the interstitial site between 20 and 25�0, and extra bristles at the posterior site rose to a maximum at 30�0; in strain 71 only tho maximum for the anterior site at 16�C was observed; strain 73 had very few additional bristles at any site over the entire temperature range. Modification of the size of the flies by growing them under crowded conditions or by enriching the modium had no effect on the pattern of the temperature response.