Implantable computer-controlled adaptive multielectrode positioning system

Acute neuronal recordings performed with metal microelectrodes in nonhuman primates allow investigating the neural substrate of complex cognitive behaviors. Yet the daily reinsertion and positioning of the electrodes prevents recording from many neurons simultaneously, limiting the suitability of these types of recordings for brain-computer interface applications or for large-scale population statistical methods on a trial-by-trial basis. In contrast, chronically implanted multielectrode arrays offer the opportunity to record from many neurons simultaneously, but immovable electrodes prevent optimization of the signal during and after implantation and cause the tissue response to progressively impair the transduced signal quality, thereby limiting the number of different neurons that can be recorded over the lifetime of the implant. Semichronically implanted matrices of electrodes, instead, allow individually movable electrodes in depth and achieve higher channel count compared with acute methods, hence partially overcoming these limitations. Existing semichronic systems with higher channel count lack computerized control of electrode movements, leading to limited user-friendliness and uncertainty in depth positioning. Here we demonstrate a chronically implantable adaptive multielectrode positioning system with detachable drive for computerized depth adjustment of individual electrodes over several millimeters. This semichronic 16-channel system is designed to optimize the simultaneous yield of units in an extended period following implantation since the electrodes can be independently depth adjusted with minimal effort and their signal quality continuously assessed. Importantly, the electrode array is designed to remain within a chronic recording chamber for a prolonged time or can be used for acute recordings with high signal-to-noise ratio in the cerebral cortex of nonhuman primates.

NEW & NOTEWORTHY We present a 16-channel motorized, semichronic multielectrode array with individually depth-adjustable electrodes to record in the cerebral cortex of nonhuman primates. Compared with fixed-geometry arrays, this system allows repeated reestablishing of single neuron isolation. Compared with manually adjustable arrays it benefits from computer-controlled positioning. Compared with motorized semichronic systems it allows higher channel counts due to a robotic single actuator approach. Overall the system is designed to optimize the simultaneous yield of units over the course of implantation.

Large-scale, high-resolution electrophysiological imaging of field potentials in brain slices with microelectronic multielectrode arrays

Multielectrode arrays (MEAs) are extensively used for electrophysiological studies on brain slices, but the spatial resolution and field of recording of conventional arrays are limited by the low number of electrodes available. Here, we present a large-scale array recording simultaneously from 4096 electrodes used to study propagating spontaneous and evoked network activity in acute murine cortico-hippocampal brain slices at unprecedented spatial and temporal resolution. We demonstrate that multiple chemically induced epileptiform episodes in the mouse cortex and hippocampus can be classified according to their spatio-temporal dynamics. Additionally, the large-scale and high-density features of our recording system enable the topological localization and quantification of the effects of antiepileptic drugs in local neuronal microcircuits, based on the distinct field potential propagation patterns. This novel high-resolution approach paves the way to detailed electrophysiological studies in brain circuits spanning spatial scales from single neurons up to the entire slice network.

Cortico-hippocampal hyperexcitability in synapsin I/II/III knockout mice: age-dependency and response to the antiepileptic drug levetiracetam

Synapsins (SynI, SynII, SynIII) are a multigene family of synaptic vesicle (SV) phosphoproteins implicated in the regulation of synaptic transmission and plasticity. Synapsin I, II, I/II and I/II/III knockout mice are epileptic and SYN1/2 genes have been identified as major epilepsy susceptibility genes in humans. We analyzed cortico-hippocampal epileptiform activity induced by 4-aminopyridine (4AP) in acute slices from presymptomatic (3-weeks-old) and symptomatic (1-year-old) Syn I/II/III triple knockout (TKO) mice and aged-matched triple wild type (TWT) controls and assessed the effect of the SV-targeted antiepileptic drug (AED) levetiracetam (LEV) in reverting the epileptic phenotype. Both fast and slow interictal (I-IC) and ictal (IC) events were observed in both genotypes. The incidence of fast I-IC events was higher in presymptomatic TKO slices, while frequency and latency of I-IC events were similar in both genotypes. The major age and genotype effects were observed in IC activity, that was much more pronounced in 3-weeks-old TKO and persisted with age, while it disappeared from 1-year-old TWT slices. LEV virtually suppressed fast I-IC and IC discharges from 3-weeks-old TWT slices, while it only increased the latency of fast I-IC and IC activity in TKO slices. Analysis of I-IC events in patch-clamped CA1 pyramidal neurons revealed that LEV increased the inhibitory/excitatory ratio of I-IC activity in both genotypes. The lower LEV potency in TKO slices of both ages was associated with a decreased expression of SV2A, a SV protein acting as LEV receptor, in cortex and hippocampus. The results demonstrate that deletion of Syn genes is associated with a higher propensity to 4AP-induced epileptic paroxysms that precedes the onset of epilepsy and consolidates with age. LEV ameliorates such hyper excitability by enhancing the inhibition/excitation ratio, although the effect is hindered in TKO slices which exhibit a concomitant decrease in the levels of the LEV receptor SV2A.