No abstract

Classical work in squid axon reports resting membrane potential is independent of temperature, but our findings suggest that this is not the case for axons in mammalian optic nerve. Refractory period duration changes over 10 times between 37 °C and room temperature, and afterpotential polarity is also acutely temperature sensitive, inconsistent with changes in temperature impacting nerve function only through altered rates of ion channel gating kinetics. Our evidence suggests that the membrane potential is enhanced by warming, an effect reduced by exposure to ouabain. The temperature dependence can be explained if axonal Na(+)/K(+) ATPase continuously expels Na(+) ions that enter axons largely electroneutrally, thereby adding a substantial electrogenic component to the membrane potential. Block of the Na(+) transporter NKCC1 with bumetanide increases refractoriness, like depolarization, indicating that this is a probable route by which Na(+) enters, raising the expectation that the rate of electroneutral Na(+) influx increases with temperature and suggesting a temperature-dependent transmembrane Na(+) cycle that contributes to membrane potential.

1Reading is a rapid, distributed process that engages multiple components of the 2 ventral visual stream. However, the neural constituents and their interactions that allow 3 us to identify written words are not well understood. Using direct intracranial recordings 4 in a large cohort of humans, we comprehensively isolated the spatiotemporal 5 dynamics of visual word recognition across the entire left ventral occipitotemporal 6 cortex. The mid-fusiform cortex is the first region that is sensitive to word identity and 7 to both sub-lexical and lexical frequencies. Its activation, response latency and 8 amplitude, are highly dependent on the statistics of natural language. Information 9 about lexicality and word frequency propagates posteriorly from this region to 10 traditional visual word form regions and to earlier visual cortex. This unique sensitivity 11 of mid-fusiform cortex to the lexical characteristics of written words points to its central 12 role as an orthographic lexicon, which accesses the long-term memory 13representations of visual word forms. 14 Woodhead et al., 2014) to enable rapid orthographic-lexical-semantic transformations. 36While most of our knowledge of the cortical architecture of reading arises from 37 functional MRI, the rapid speed of reading demands that we use methods with very 38 high spatiotemporal resolution to study these processes. To this end, we used 39 recordings in 35 individuals with 784 intracranial electrodes, to comprehensively 40 characterize the spatial organization and functional roles of orthographic and lexical 41 regions across the ventral visual pathway during sub-lexical and lexical processes. 42Given their construction, these two tasks, performed in the same cohort, tap into 43 varying levels of attentional modulation of orthographic processing. Specifically, we 44 isolated functionally distinct regions across the vOTC that are highly sensitive to the 45 structure and statistics of natural language at multiple stages of orthographic 46 processing. 47

The contribution of insular cortex to speech production remains unclear and controversial given diverse findings from functional neuroimaging and lesional data. To create a precise spatiotemporal map of insular activity, we performed a series of experiments: single-word articulations of varying complexity, non-speech orofacial movements and speech listening, in a cohort of 27 patients implanted with penetrating intracranial electrodes. The posterior insula was robustly active bilaterally, but after the onset of articulation, during listening to speech and during production of non-speech mouth movements. Preceding articulation there was very sparse activity, localized primarily to the frontal operculum rather than the insula. Posterior insular was active coincident with superior temporal gyrus but was more active for self-generated speech than external speech, the opposite of the superior temporal gyrus. These findings support the conclusion that the insula does not serve pre-articulatory preparatory roles.