Postural support requirements preferentially modulate late components of the gastrocnemius response to transcranial magnetic stimulation.

Mounting evidence suggests that motor evoked potentials (MEPs) recorded in upper limb muscles with postural support roles following transcranial magnetic stimulation receive contributions from both corticospinal and non-corticospinal descending pathways. We tested the hypothesis that neural structures responsible for regulating upright balance are involved in transmitting late portions of TMS-induced MEPs in a lower limb muscle. MEPs were recorded in the medial gastrocnemius muscles of each leg, while participants supported their upright posture in five postural conditions that required different levels of support from the target muscles. We observed that early and late portions of the MEP were modulated independently, with early MEP amplitude being reduced when high levels of postural support were required from a target muscle. Independent modulation of early and late MEPs by altered postural demand suggests largely separable transmission of each part of the MEP. The early component of the MEP is likely generated by fast-conducting corticospinal pathways, whereas the later component may be primarily transmitted along a polysynaptic cortico-reticulospinal pathway.

Investigating the effect of forestry on leaf-litter arthropods (Algonquin Park, Ontario, Canada).

Arthropods are the most diverse taxonomic group of terrestrial eukaryotes and are sensitive to physical alterations in their environment such as those caused by forestry. With their enormous diversity and physical omnipresence, arthropods could be powerful indicators of the effects of disturbance following forestry. When arthropods have been used to measure the effects of disturbance, the total diversity of some groups is often found to increase following forestry. However, these findings are frequently derived using a coarse taxonomic grain (family or order) to accommodate for various taxonomic impediments (including cryptic diversity and poorly resourced taxonomists). Our intent with this work was to determine the diversity of arthropods in and around Algonquin Park, and how this diversity was influenced by disturbance (in this case, forestry within the past 25 years). We used DNA barcode-derived diversity estimates (Barcode Index Number (BIN) richness) to avoid taxonomic impediments and as a source of genetic information with which we could conduct phylogenetic estimates of diversity (PD). Diversity patterns elucidated with PD are often, but not always congruent with taxonomic estimates-and departures from these expectations can help clarify disturbance effects that are hidden from richness studies alone. We found that BIN richness and PD were greater in disturbed (forested) areas, however when we controlled for the expected relationship between PD and BIN richness, we found that cut sites contained less PD than expected and that this diversity was more phylogenetically clustered than would be predicted by taxonomic richness. While disturbance may cause an evident increase in diversity, this diversity may not reflect the full evolutionary history of the assemblage within that area and thus a subtle effect of disturbance can be found decades following forestry.