A Force on the Crown and Tug of War in the Periodontal Complex.

The load-bearing dentoalveolar fibrous joint is composed of biomechanically active periodontal ligament (PDL), bone, cementum, and the synergistic entheses of PDL-bone and PDL-cementum. Physiologic and pathologic loads on the dentoalveolar fibrous joint prompt natural shifts in strain gradients within mineralized and fibrous tissues and trigger a cascade of biochemical events within the widened and narrowed sites of the periodontal complex. This review highlights data from in situ biomechanical simulations that provide tooth movements relative to the alveolar socket. The methods and subsequent results provide a reasonable approximation of strain-regulated biochemical events resulting in mesial mineral formation and distal resorption events within microanatomical regions at the ligament-tethered/enthesial ends. These biochemical events, including expressions of biglycan, decorin, chondroitin sulfated neuroglial 2, osteopontin, and bone sialoprotein and localization of various hypertrophic progenitors, are observed at the alkaline phosphatase-positive widened site, resulting in mineral formation and osteoid/cementoid layers. On the narrowed side, tartrate-resistant acid phosphatase regions can lead to a sequence of clastic activities resulting in resorption pits in bone and cementum. These strain-regulated biochemical and subsequently biomineralization events in the load-bearing periodontal complex are critical for maintenance of the periodontal space and overall macroscale joint biomechanics.

The 'when' and 'where' of semantic coding in the anterior temporal lobe: Temporal representational similarity analysis of electrocorticogram data.

Electrocorticograms (ECoG) provide a unique opportunity to monitor neural activity directly at the cortical surface. Ten patients with subdural electrodes covering ventral and lateral anterior temporal regions (ATL) performed a picture naming task. Temporal representational similarity analysis (RSA) was used, for the first time, to compare spatio-temporal neural patterns from the ATL surface with pre-defined theoretical models. The results indicate that the neural activity in the ventral subregion of the ATL codes semantic representations from 250 msec after picture onset. The observed activation similarity was not related to the visual similarity of the pictures or the phonological similarity of their names. In keeping with convergent evidence for the importance of the ATL in semantic processing, these results provide the first direct evidence of semantic coding from the surface of the ventral ATL and its time-course.