The oxygenation response to functional stimulation: is there a physiological meaning to the lag between parameters?

To investigate the regulation of the hemodynamic response to functional stimulation, functional near-infrared spectroscopy (fNIRS) has been used, due to its ability to assess the dynamics of oxygenated, deoxygenated and total hemoglobin concentration ([oxy-Hb], [deoxy-Hb] and [tot-Hb]). Concerning the latency of these parameters, recent studies have returned a consistent picture when comparing the oxygenation response in the sensorimotor to the visual system: changes in [oxy-Hb] lead those in [deoxy-Hb] by 1.6 ± 0.2 s (mean ± SD) for the sensorimotor system but not for the visual system (0.1 ± 0.3 s). A number of physiological differences between these cortical areas may account for such a discrepancy, however, the methodological properties of transcranial NIRS also have a relevant influence. Here we show that for the motor system the latency between changes in oxy- compared to deoxy-Hb vanishes once efforts are made to reduce the effects of a systemic response accompanying sensorimotor activity. We apply two independent approaches to reduce the systemic response and find a simultaneous change in [oxy-Hb] and [deoxy-Hb] even in response to a motor paradigm. The two approaches are: (i) an experimental paradigm with alternating contralateral and ipsilateral motor performance without interspersed rest periods designed to minimize systemic changes and (ii) a global correction scheme in an experiment, comparing a unilateral motor performance to rest. These data shed some doubt on the alleged fundamental physiological difference between cortical hemodynamic regulation in motor and visual cortex and highlight the relevance to respect contributions of the systemic hemodynamics

Towards a complete in silico assessment of the outcome of cochlear implantation surgery

Cochlear implantation (CI) surgery is a very successful technique, performed on more than 300,000 people worldwide. However, since the challenge resides in obtaining an accurate surgical planning, computational models are considered to provide such accurate tools. They allow us to plan and simulate beforehand surgical procedures in order to maximally optimize surgery outcomes, and consequently provide valuable information to guide pre-operative decisions. The aim of this work is to develop and validate computational tools to completely assess the patient-specific functional outcome of the CI surgery. A complete automatic framework was developed to create and assess computationally CI models, focusing on the neural response of the auditory nerve fibers (ANF) induced by the electrical stimulation of the implant. The framework was applied to evaluate the effects of ANF degeneration and electrode intra-cochlear position on nerve activation. Results indicate that the intra-cochlear positioning of the electrode has a strong effect on the global performance of the CI. Lateral insertion provides better neural responses in case of peripheral process degeneration, and it is recommended, together with optimized intensity levels, in order to preserve the internal structures. Overall, the developed automatic framework provides an insight into the global performance of the implant in a patient-specific way. This enables to further optimize the functional performance and helps to select the best CI configuration and treatment strategy for a given patient.This work was financially supported by the European Commission (FP7 project number 304857, HEAR-EU), Generalitat de Catalunya (PRODUCTE program, project number 2016PROD00047) and the Spanish Ministry of Economy and Competitiveness under the Maria de Maeztu Units of Excellence Programme (MDM-2015-0502)