Membrane resistance and shunting inhibition: where biophysics meets state-dependent human neurophysiology

Activation of neurons not only changes their membrane potential and firing rate but, as a secondary action reduces membrane resistance. This loss of resistance, or increase of conductance, may be of central importance in non-invasive magnetic or electric stimulation of the human brain since electrical fields cause larger changes in transmembrane voltage in resting neurones with low membrane conductances than in active neurones with high conductance. This may explain why both the immediate and after-effects of brain stimulation are smaller or even reversed during voluntary activity compared to rest. Membrane conductance is also increased during shunting inhibition, which accompanies the classic GABAa IPSP. This short-circuits nearby EPSPs and is suggested here to contribute to the magnitude and time course of short latency intracortical inhibition (SICI) and facilitation (ICF). This article is protected by copyright. All rights reserved

Cash-Flow and Savings Practices of Low-Income Households: Evidence From a Follow-Up Study of IDA Participants

This study uses a survey of participants from an Individual Development Account (IDA) matched savings intervention to examine self-reported financial practices (cash flow and savings) five years after the intervention terminated. Latent class analysis produced three groups of financial practices - high, medium, and low functioning. Results showed that some low-income households are carefully managing their finances. Psychological sense of mastery was positively related to high functioning cash-flow and savings. The IDA intervention had no association with latent class membership. Antipoverty interventions should assess the financial practices of participants at the time of service enrollment. Further, social service providers should not assume that households are not already carefully managing their finances

Preconditioning of low-frequency repetitive transcranial magnetic stimulation with transcranial direct current stimulation: evidence for homeostatic plasticity in the human motor cortex

Recent experimental work in animals has emphasized the importance of homeostatic plasticity as a means of stabilizing the properties of neuronal circuits. Here, we report a phenomenon that indicates a homeostatic pattern of cortical plasticity in healthy human subjects. The experiments combined two techniques that can produce long-term effects on the excitability of corticospinal output neurons: transcranial direct current stimulation (TDCS) and repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex. "Facilitatory preconditioning" with anodal TDCS caused a subsequent period of 1 Hz rTMS to reduce corticospinal excitability to below baseline levels for >20 min. Conversely, "inhibitory preconditioning" with cathodal TDCS resulted in 1 Hz rTMS increasing corticospinal excitability for at least 20 min. No changes in excitability occurred when 1 Hz rTMS was preceded by sham TDCS. Thus, changing the initial state of the motor cortex by a period of DC polarization reversed the conditioning effects of 1 Hz rTMS. These preconditioning effects of TDCS suggest the existence of a homeostatic mechanism in the human motor cortex that stabilizes corticospinal excitability within a physiologically useful range

Weissistachys Kentuckiensis: A new Name for Weissia Kentuckiense Rothwell and Taylor

This is the publisher's version, also available electronically from www.jstor.org.The generic name Weissia Roth well and Taylor is determined to be a later homonym of Weissia Hedwig. Weissia Rothwell and Taylor is therefore renamed Weissistachys, and the appropriate name transfer is made for the type species, Weissistachys kentuckiensis (Rothwell et Taylor) comb. nov

Studies of Paleozoic Calamitean Cones: Weissia Kentuckiense Gen. et Sp. Nov.

This is the publisher's version, also available electronically from http://www.jstor.org.The recent discovery of a new petrified fructification from the Lewis Creek coal ball locality in eastern Kentucky adds to our knowledge of the structure and diversity of c alamitean cones. The incomplete specimen measures 4.8 cm long and 6.0 mm in diameter, and is composed of alternating bract and sporangiophore whorls. Approximately 24 bracts are present in each whorl. Bracts arise at right angles to the axis and are fused into a shallow disk for 2.0 mm before arching distally and becoming free. Six sporangiophores arise obliquely from slightly above each bract disk; each sporangiophore bears two large pendant sporangia that are attached along their distal and tangential surfaces. Sporangia! walls are a single cell layer thick and are characterized by internal cell lumen partitions. The distal ends of the sporangiophores are fused to form a continuous ring of tissue that surrounds the sporangia. Features of the new cone are discussed in relation to those of other calamitean cones of similar age

Possible role of backpropagating action potentials in corticospinal neurons in I-wave periodicity following a TMS pulse

A single pulse of TMS or direct electric stimulation over M1 causes repetitive synchronized firing of corticospinal tract (CST) neurons. Two mechanisms for the repetitive firing have been proposed: a cascade of synaptic inputs to the pyramidal neurons and a single reverberating circuit of interneurons. Here, we propose another possibility in which bursting of CST neurons is produced by dendritic Ca2+-spikes. Backpropagation of the initial action potential (I1-wave) from the soma interacts with synaptic input in the dendrites to initiate a dendritic calcium spike. These Ca2+-spikes produce a burst of somatic action potentials that starts about 1.5 ms after the initial discharge of the neuron, which may produce the later I-waves

Perceived Impact of Individual Development Account Participation Among Native Hawaiians

Indigenous peoples face many social development challenges and the lingering effects of colonization. Income transfer, a traditional social welfare approach designed to raise minimum living standards, has had limited beneficial effects on long-term social conditions. As a complement to income transfer, asset-based approaches to social welfare have resulted in positive effects in the short and long terms. Some Indigenous communities are exploring how asset-based interventions might enhance social development (Hicks, Edwards, Dennis, & Finsel, 2005), but only limited and scattered research describes how they experience asset-building programs. This qualitative descriptive study explores the perceived impact of a large Individual Development Account (IDA) program for Indigenous Native Hawaiians. Data consist of answers to open-ended questions about the impacts of participating in an IDA program. Participants felt that the culturally based program material was empowering and that they gained lasting, meaningful life skills. They attributed skills development, psychological changes, and tangible asset gains to the IDA program. Notably, participants who did not finish the program identified barriers to doing so, including a lack of flexibility in savings requirements and life events that forced an exit from the program