Spiking Neurons Learning Phase Delays

Time differences between the two ears are an important cue for animals to azimuthally locate a sound source. The first binaural brainstem nucleus, in mammals the medial superior olive, is generally believed to perform the necessary computations. Its cells are sensitive to variations of interaural time differences of about 10 μs. The classical explanation of such a neuronal time-difference tuning is based on the physical concept of delay lines. Recent data, however, are inconsistent with a temporal delay and rather favor a phase delay. By means of a biophysical model we show how spike-timing-dependent synaptic learning explains precise interplay of excitation and inhibition and, hence, accounts for a physical realization of a phase delay

The sound of concepts: The link between auditory and conceptual brain systems

Concepts in long-term memory are important building blocks of human cognition and are the basis for object recognition, language and thought. While it is well accepted that concepts are comprised of features related to sensory object attributes, it is still unclear how these features are represented in the brain. Of central interest is whether concepts are essentially grounded in perception. This would imply a common neuroanatomical substrate for perceptual and conceptual processing. Here we show using functional magnetic resonance imaging and recordings of event-related potentials that acoustic conceptual features rapidly recruit auditory areas even when implicitly presented through visual words. Recognizing words denoting objects for which acoustic features are highly relevant (e.g. "telephone") suffices to ignite cell assemblies in the posterior superior and middle temporal gyrus (pSTG/MTG) that were also activated by listening to real sounds. Activity in pSTG/MTG had an onset of 150 ms and increased parametrically as a function of acoustic feature relevance. Both findings suggest a conceptual origin of this effect rather than post-conceptual strategies such as imagery. The presently demonstrated link between auditory and conceptual brain systems parallels observations in other memory systems suggesting that modality-specificity represents a general organizational principle in cortical memory representation. The understanding of concepts as a partial reinstatement of brain activity during perception stresses the necessity of rich sensory experiences for concept acquisition. The modality-specific nature of concepts could also explain the difficulties in achieving a consensus about overall definitions of abstract concepts such as freedom or justice unless embedded in a concrete, experienced situation

Report

Information about the position of sensory objects and identifying their concurrent behavioral relevance is vital to navigate the environment. In the auditory system, spatial information is computed in the brain based on the position of the sound source relative to the observer and thus assumed to be egocentric throughout the auditory pathway. This assumption is largely based on studies conducted in either anesthetized or head-fixed and passively listening animals, thus lacking self-motion and selective listening. Yet these factors are fundamental components of natural sensing' that may crucially impact the nature of spatial coding and sensory object representation.(2) How individual objects are neuronally represented during unrestricted self-motion and active sensing remains mostly unexplored. Here, we trained gerbils on a behavioral foraging paradigm that required localization and identification of sound sources during free navigation. Chronic tetrode recordings in primary auditory cortex during task performance revealed previously unreported sensory object representations. Strikingly, the egocentric angle preference of the majority of spatially sensitive neurons changed significantly depending on the task-specific identity (outcome association) of the sound source. Spatial tuning also exhibited large temporal complexity. Moreover, we encountered egocentrically untuned neurons whose response magnitude differed between source identities. Using a neural network decoder, we show that, together, these neuronal response ensembles provide spatiotemporally co-existent information about both the egocentric location and the identity of individual sensory objects during self-motion, revealing a novel cortical computation principle for naturalistic sensing

BIOHYBRID – Biohybrid templates for peripheral nerve regeneration

[Excerpt] Peripheral nerve injuries represent a major cause for morbidity and disability in affected patients and cause substantial costs for society in a global perspective. It has been estimated that peripheral nerve injuries affect 2.8% of trauma patients,many of whom acquire life-long disability (Noble et al., 1998). With respect to an incidence of nerve injuries of 13.9/100,000 inhabitants per year (Asplund et al., 2009) and the number of inhabitants in the EU (495,000,000 inhabitants in 2007), the number of peripheral nerve injuries requiring repair and reconstruction, excluding nerve injuries by amputations, may be 70,000 annually only in EU countries. Related to peripheral nerve injuries, the costs for society are substantial and consist of direct (costs for surgery, outpatient visits and rehabilitation) and indirect (lost production) costs. Individual median and ulnar nerve injuries in the forearm have total costs of EUR 51,000 and 31,000, respectively, where around 85% of the costs consist of loss of production (Rosberg et al., 2005), still excluding costs for adjusted quality of life ( Eriksson et al., 2011) . Thus, one may estimate that the annual costs only in the EU may be as high as EUR 2.2 billion, indicating that improved treatment strategies for peripheral nerve injuries may not only improve the situation for patients, but may also significantly reduce costs for society. [...](undefined

Regeneration of long-distance peripheral nerve defects after delayed reconstruction in healthy and diabetic rats is supported by immunomodulatory chitosan nerve guides

Background: Delayed reconstruction of transection or laceration injuries of peripheral nerves is inflicted by a reduced regeneration capacity. Diabetic conditions, more frequently encountered in clinical practice, are known to further impair regeneration in peripheral nerves. Chitosan nerve guides (CNGs) have recently been introduced as a new generation of medical devices for immediate peripheral nerve reconstruction. Here, CNGs were used for 45 days delayed reconstruction of critical length 15 mm rat sciatic nerve defects in either healthy Wistar rats or diabetic Goto-Kakizaki rats; the latter resembling type 2 diabetes. In short and long-term investigations, we comprehensively analyzed the performance of one-chambered hollow CNGs (hCNGs) and two-chambered CNGs (CFeCNGs) in which a chitosan film has been longitudinally introduced. Additionally, we investigated in vitro the immunomodulatory effect provided by the chitosan film. Results: Both types of nerve guides, i.e. hCNGs and CFeCNGs, enabled moderate morphological and functional nerve regeneration after reconstruction that was delayed for 45 days. These positive findings were detectable in generally healthy as well as in diabetic Goto-Kakizaki rats (for the latter only in short-term studies). The regenerative outcome did not reach the degree as recently demonstrated after immediate reconstruction using hCNGs and CFeCNGs. CFeCNG-treatment, however, enabled tissue regrowth in all animals (hCNGs: only in 80% of animals). CFeCNGs did further support with an increased vascularization of the regenerated tissue and an enhanced regrowth of motor axons. One mechanism by which the CFeCNGs potentially support successful regeneration is an immunomodulatory effect induced by the chitosan film itself. Our in vitro results suggest that the pro-regenerative effect of chitosan is related to the differentiation of chitosan-adherent monocytes into pro-healing M2 macrophages. Conclusions: No considerable differences appear for the delayed nerve regeneration process related to healthy and diabetic conditions. Currently available chitosan nerve grafts do not support delayed nerve regeneration to the same extent as they do after immediate nerve reconstruction. The immunomodulatory characteristics of the biomaterial may, however, be crucial for their regeneration supportive effects