Neef, Andreas

[["dc.bibliographiccitation.artnumber","e0132577"],["dc.bibliographiccitation.issue","7"],["dc.bibliographiccitation.journal","PloS one"],["dc.bibliographiccitation.volume","10"],["dc.contributor.author","Stern, Shani"],["dc.contributor.author","Agudelo-Toro, Andres"],["dc.contributor.author","Rotem, Assaf"],["dc.contributor.author","Moses, Elisha"],["dc.contributor.author","Neef, Andreas"],["dc.date.accessioned","2019-07-09T11:41:25Z"],["dc.date.available","2019-07-09T11:41:25Z"],["dc.date.issued","2015"],["dc.description.abstract","Excitation of neurons by an externally induced electric field is a long standing question that has recently attracted attention due to its relevance in novel clinical intervention systems for the brain. Here we use patterned quasi one-dimensional neuronal cultures from rat hippocampus, exploiting the alignment of axons along the linear patterned culture to separate the contribution of dendrites to the excitation of the neuron from that of axons. Network disconnection by channel blockers, along with rotation of the electric field direction, allows the derivation of strength-duration (SD) curves that characterize the statistical ensemble of a population of cells. SD curves with the electric field aligned either parallel or perpendicular to the axons yield the chronaxie and rheobase of axons and dendrites respectively, and these differ considerably. Dendritic chronaxie is measured to be about 1 ms, while that of axons is on the order of 0.1 ms. Axons are thus more excitable at short time scales, but at longer time scales dendrites are more easily excited. We complement these studies with experiments on fully connected cultures. An explanation for the chronaxie of dendrites is found in the numerical simulations of passive, realistically structured dendritic trees under external stimulation. The much shorter chronaxie of axons is not captured in the passive model and may be related to active processes. The lower rheobase of dendrites at longer durations can improve brain stimulation protocols, since in the brain dendrites are less specifically oriented than axonal bundles, and the requirement for precise directional stimulation may be circumvented by using longer duration fields."],["dc.identifier.doi","10.1371/journal.pone.0132577"],["dc.identifier.pmid","26186201"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/12025"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/58422"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1932-6203"],["dc.rights","CC BY 4.0"],["dc.rights.uri","https://creativecommons.org/licenses/by/4.0"],["dc.title","Chronaxie Measurements in Patterned Neuronal Cultures from Rat Hippocampus."],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","026019"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Journal of Neural Engineering"],["dc.bibliographiccitation.volume","10"],["dc.contributor.author","Agudelo-Toro, Andres"],["dc.contributor.author","Neef, Andreas"],["dc.date.accessioned","2018-11-07T09:26:42Z"],["dc.date.available","2018-11-07T09:26:42Z"],["dc.date.issued","2013"],["dc.description.abstract","Objective. We present a computational method that implements a reduced set of Maxwell's equations to allow simulation of cells under realistic conditions: sub-micron cell morphology, a conductive non-homogeneous space and various ion channel properties and distributions. Approach. While a reduced set of Maxwell's equations can be used to couple membrane currents to extra-and intracellular potentials, this approach is rarely taken, most likely because adequate computational tools are missing. By using these equations, and introducing an implicit solver, numerical stability is attained even with large time steps. The time steps are limited only by the time development of the membrane potentials. Main results. This method allows simulation times of tens of minutes instead of weeks, even for complex problems. The extracellular fields are accurately represented, including secondary fields, which originate at inhomogeneities of the extracellular space and can reach several millivolts. We present a set of instructive examples that show how this method can be used to obtain reference solutions for problems, which might not be accurately captured by the traditional approaches. This includes the simulation of realistic magnitudes of extracellular action potential signals in restricted extracellular space. Significance. The electric activity of neurons creates extracellular potentials. Recent findings show that these endogenous fields act back onto the neurons, contributing to the synchronization of population activity. The influence of endogenous fields is also relevant for understanding therapeutic approaches such as transcranial direct current, transcranial magnetic and deep brain stimulation. The mutual interaction between fields and membrane currents is not captured by today's concepts of cellular electrophysiology, including the commonly used activation function, as those concepts are based on isolated membranes in an infinite, isopotential extracellular space. The presented tool makes simulations with detailed morphology and implicit interactions of currents and fields available to the electrophysiology community."],["dc.identifier.doi","10.1088/1741-2560/10/2/026019"],["dc.identifier.isi","000316728700020"],["dc.identifier.pmid","23503026"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9447"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30360"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Iop Publishing Ltd"],["dc.relation.issn","1741-2560"],["dc.rights","CC BY-NC-SA 3.0"],["dc.rights.uri","https://creativecommons.org/licenses/by-nc-sa/3.0"],["dc.title","Computationally efficient simulation of electrical activity at cell membranes interacting with self-generated and externally imposed electric fields"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","e86794"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","PLoS ONE"],["dc.bibliographiccitation.volume","9"],["dc.contributor.author","Rotem, Assaf"],["dc.contributor.author","Neef, Andreas"],["dc.contributor.author","Neef, Nicole E."],["dc.contributor.author","Agudelo-Toro, Andres"],["dc.contributor.author","Rakhmilevitch, David"],["dc.contributor.author","Paulus, Walter J."],["dc.contributor.author","Moses, Elisha"],["dc.date.accessioned","2019-07-09T11:39:39Z"],["dc.date.available","2019-07-09T11:39:39Z"],["dc.date.issued","2014"],["dc.description.abstract","Transcranial Magnetic Stimulation (TMS) is a promising technology for both neurology and psychiatry. Positive treatment outcome has been reported, for instance in double blind, multi-center studies on depression. Nonetheless, the application of TMS towards studying and treating brain disorders is still limited by inter-subject variability and lack of model systems accessible to TMS. The latter are required to obtain a deeper understanding of the biophysical foundations of TMS so that the stimulus protocol can be optimized for maximal brain response, while inter-subject variability hinders precise and reliable delivery of stimuli across subjects. Recent studies showed that both of these limitations are in part due to the angular sensitivity of TMS. Thus, a technique that would eradicate the need for precise angular orientation of the coil would improve both the inter-subject reliability of TMS and its effectiveness in model systems. We show here how rotation of the stimulating field relieves the angular sensitivity of TMS and provides improvements in both issues. Field rotation is attained by superposing the fields of two coils positioned orthogonal to each other and operated with a relative phase shift in time. Rotating field TMS (rfTMS) efficiently stimulates both cultured hippocampal networks and rat motor cortex, two neuronal systems that are notoriously difficult to excite magnetically. This opens the possibility of pharmacological and invasive TMS experiments in these model systems. Application of rfTMS to human subjects overcomes the orientation dependence of standard TMS. Thus, rfTMS yields optimal targeting of brain regions where correct orientation cannot be determined (e.g., via motor feedback) and will enable stimulation in brain regions where a preferred axonal orientation does not exist."],["dc.identifier.doi","10.1371/journal.pone.0086794"],["dc.identifier.fs","601988"],["dc.identifier.pmid","24505266"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10031"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/58019"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1932-6203"],["dc.rights","CC BY 4.0"],["dc.rights.uri","https://creativecommons.org/licenses/by/4.0"],["dc.title","Solving the Orientation Specific Constraints in Transcranial Magnetic Stimulation by Rotating Fields"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]