Intracortical microelectrodes puncture the intact pia mater membrane during insertion, a process that can cause brain dimpling and trauma. To ensure that the device is able to withstand forces during implantation without buckling, the selection of acceptable implant materials and geometries is limited to rigid designs with large cross-sectional areas. Such designs likely increase insertion trauma and potentially exacerbate the chronic tissue response. In this paper, a technique that may relax the mechanical requirements of implanted microelectrodes through enzymatic (collagenase mediated) manipulation of the pia mater is quantified experimentally. Measurements of the insertion force profiles were obtained with a load cell during computer controlled (10 microm/s) insertion of microwire arrays into the cortex of rats. It was observed that collagenase application reduced the peak insertion force experienced by the microwire arrays by almost 40% on average (4.04 +/-2.03 mN versus 2.36 +/-1.17 mN; control versus treated sites). Peak insertion force magnitudes were highly dependent on implant location with anterior sites registering lower peaks than more posterior sites. Chronic neural recording performance (up to one month) did not appear to be adversely affected by the collagenase treatment, suggesting the overall safety of the technique. Our data suggest that controlled application of collagenase is a useful method in enabling implantation of thinner microelectrodes, potentially facilitating reduced insertion trauma and lower immune response. Furthermore, due to dependence of insertion force on anatomical location, the intended target region should be considered in implant design.
Intracortical microelectrode arrays record multi-unit extracellular activity for neurophysiology studies and for brain-machine interface applications. The common first step is neural spike detection; a process complicated by common-noise signals from motion artifacts, electromyographic activity, and electric field pickup, especially in awake/behaving subjects. Often common-noise spikes are very similar to neural spikes in their magnitude, spectral, and temporal features. Provided sufficient spacing exists between electrodes of the array, a local neural spike is rarely recorded on multiple electrodes simultaneously. This is not true for distant common-noise sources. Two new techniques compatible with standard spike detection schemes are introduced and evaluated. The first method, virtual referencing (VR), takes the average recording from all functional electrodes in the array (represents the signal from a virtual electrode at the array's center) and subtracts it from the test electrode signal. The second method, inter-electrode correlation (IEC), computes a correlation coefficient between threshold exceeding candidate spike segments on the test electrode and concurrent segments from remaining electrodes. When sufficient correlation is detected, the candidate spike is rejected as originating from a distant common-noise source. The performance of these algorithms was compared with standard thresholding and differential referencing approaches using neural recordings from unanaesthetized rats. By evaluating characteristics of mean-spike waveforms generated by each method under different levels of common-noise, it was found that IEC consistently offered the most robust means of neural spike-detection. Furthermore, IEC's rejection of supra-threshold events not likely originating from local neurons significantly reduces data handling for downstream spike sorting and processing operations.
Implanted intra-cortical micro-electrode arrays record multi-unit extracellular spike activity that is used in deciphering the neural basis for adaptation, learning, plasticity and as command signal for brain-machine interfaces (BMI). Detection of spike activity is the first step in successful implementation of all the aforementioned applications. However, with awake and behaving animals, micro-electrode arrays typically also record non-neuronal signals induced by the animal's movement, feeding and grooming actions. The spectral and temporal nature of these artifacts is similar to neural spikes, which complicates accurate detection. The distal source and higher strength of non-neuronal signals result in their near simultaneous registration on most electrodes, while neural spiking event is rarely recorded on more than one electrode of an array. This difference is utilized in identifying non-neuronal content from acquired data by performing a correlation analysis. The efficacy of the method is evaluated by comparing outcomes from algorithms that use absolute threshold and Principal Component Analysis (PCA) as a means of identifying neural spikes with the same methods incorporating correlation analysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.