Search

ABSTRACT. C. Ghez, J. Gordon, and M. F. Ghilardi (1995; J. Gordon, M. F. Ghilardi, & C. Ghez, 1995; R. L. Sainburg, M. F. Ghilardi, H. Poizner, & C. Ghez, [...]

The purpose of this paper is to characterize the neuron-microelectrode junction, based on the equivalent electric-circuit approach. As a result, recording of action potentials can be simulated with a general-purpose circuit simulation program such as HSPICE. The response of the microelectrode was analyzed as a function of parameters such as sealing resistance and adhesion conditions. The models of the neuron and microelectrode implemented in HSPICE were first described. These models were used to simulate the behavior of the junction between a patch of neuronal membrane (described by the compartmental model) and a microelectrode. Index Terms--Circuit model, extracellular recording, Hspice simulation, microelectrode, neurons, neuro-electronic junction.

Gait and balance impairment is common in multiple sclerosis (MS), often leading to walking aids need. Rehabilitation is the most common and effective approach to tackle the burden of these symptoms, but less attention is given to the correct use of an assistive device for ambulation. Here, we aimed to maximise the effect of a rehabilitation program including walking aid training with a sensorized crutch in people with MS (PwMS). 24 PwMS (15 females, age=57.8±9.8 years, all EDSS=6) underwent a 20-session rehabilitation program focusing on gait, balance, and proper assistive device use. The experimental group (FB_group, N=12) used a crutch with real-time feedback based on user support load, whilst the control group (NOFB_group, N=12) used a standard crutch. Assessment included Timed 25 Foot Walk (T25FW), Timed Up and Go (TUG) and Modified Fatigue Impact Scale (MFIS). Moreover, functional Near-Infrared Spectroscopy (fNIRS) was used to investigate cortical activity during linear and curvilinear walking tasks. At baseline, no differences were found between groups concerning either clinical or neural evaluations. Following rehabilitation, we observed a reduction in fatigue perception in both groups (p=0.038). Moreover, FB_group performed better than NOFB_group in T25FW and TUG (p=0.028 and p=0.038, respectively). Further, after treatment, FB_group showed increased neural activity in areas involved in cognitive functions (Brodmann Areas-BA 9,10, p<0.01), multisensory integration and body representation (BA39, p=0.01) during both linear and curvilinear walking. Instead, NOFB_group showed increased activity in motor planning areas (BA 6,8, p<0.05). A significant difference was also found between groups in BA9 after treatment (FB_group>NOFBgroup, p=0.04). A 20-session rehabilitation period effectively reduces fatigue among PwMS. Moreover, a real-time feedback crutch seems to have a positive impact on walking ability. This might be due to a feedback-induced increased attention focusing on the assistive device, as suggested by the fNIRS results. [ABSTRACT FROM AUTHOR]

This paper describes computer simulations of the behavior of Hodgkin-Huxley neurons, based on a redefinition of membrane and synaptic connections as time-invariant circuit elements. Examples are given showing that this self-consistent equivalent circuit representation allows very efficient computer simulations and could facilitate the introduction of detailed biological neurons into formal neural networks. Index Terms - Neurons, synapses, time-invariant circuit models.

The purpose of this paper is to extensively analyze and utilize the key features that characterize the recently available electrophysiological technique of growing selected populations of neurons on planar substrate microelectrode arrays. This experimental configuration is first simulated by modeling the signal transduction operated by an array of microtransducers coupled to a network of Hodgkin-Huxley-like neurons, connected to each other with given levels of synaptic strength. Signal processing tools are then described and validated by identifying the various degrees of connectivity previously introduced into the simulated network. Finally, these software tools are utilized to characterize the activity and identify the synaptic connectivity of networks of cultured neurons extracted from dorsal root ganglia (DRG) of chick embryos and exposed to synapse inhibiting/reinforcing ions. As a result, correlations between various regimens of electrophysiological activity and synaptic strength are obtained. Index Terms - In vitro networks of neurons, neuronal network dynamics, planar substrate microelectrode arrays, signal-processing tools, simulated neuronal networks, synaptic connections