Contact size does not affect high frequency oscillation detection in intracerebral EEG recordings in a rat epilepsy model

Abstract

Objective-High frequency oscillations (HFOs) have been implicated in ictogenesis and epileptogenesis. The effect of contact size (in the clinical range: 1-10 mm 2 ) on HFO detection has not been determined. This study assesses the feasibility of HFO detection in a rat epilepsy model using macrocontacts and clinical amplifiers, and the effect of contact size on HFO detection within the macrocontact range.Methods-Eight epileptic rats were implanted with intracerebral electrodes containing three adjacent contacts of different sizes (0.02, 0.05 and 0.09 mm 2 ). HFOs were manually marked on 5 min interictal EEG segments. HFO rates and durations were compared between the different contacts.Results-10,966 ripples and 1475 fast ripples were identified in the recordings from 30 contacts. There were no significant differences in spike or HFO rates between the different contact sizes, nor was there a significant difference in HFO duration.Conclusions-HFOs can be detected in a rat epilepsy model using macrocontacts. Within the studied range, size did not significantly influence HFO detection.Significance-Using comparative anatomy of rat and human limbic structures, these findings suggest that reducing the size of macrocontacts (compared to those commercially available) would not improve HFO detection rates.

Electrophysiological Biomarkers of Epilepsy

“…One study found a significant reduction in the number of fast ripple-frequency HFOs recorded with standard clinical electrodes (surface area 9.4 mm 2 ) compared with microelectrodes [65]. In contrast, other experiments compared hippocampal ripple-and fast ripplefrequency HFOs recorded with electrodes of different contact sizes in epileptic rats and found no difference in HFO duration or spectral frequency with respect to electrode diameter, although the mean amplitude of all HFOs was significantly lower compared with the amplitude of HFOs recorded with microelectrodes [4,66]. In subsequent work involving patients from this same group, similar rates of HFOs were found among electrodes with surface areas between 0.2 and 5 mm 2 [67], suggesting that smaller contact diameter would not necessarily improve the detection of HFOs.…”

“…For example, ripple-and fast ripple-frequency HFOs could be recorded using clinical macroelectrode, and the volume of tissue and/or spatial distribution associated with fast-ripple frequency HFOs was larger than predicted from microelectrode recordings [65,66,100]. The link between the rates of fast ripple-frequency HFOs and SOZ was also confirmed [65,101,102], and from these studies evidence for the association of ripple-frequency HFOs and the SOZ in MTLE and neocortical epilepsies was obtained, although fast ripple-frequency HFOs appear more specific to the SOZ, particularly in MTLE [63].…”

Hochfrequenzoszillationen (80–500 Hz)

“…Wie bereits erwähnt, kann zum momentanen Zeitpunkt nicht gesagt werden, ob die Elektrodengröße und Aufzeichnungsmethode einen entscheidenden Einfluss darauf hat, dass HFO zuverlässig aufgezeichnet werden können [12,40]. [15].…”

A comparison between automated detection methods of high-frequency oscillations (80–500Hz) during seizures

“…Four stainless steel screws (2.4 mm length) were fixed to the skull and 4 small holes were drilled to allow the implantation of bipolar electrodes (20-30 k ; 30-50 mm length; distance between exposed tips: 500 m) made by twisting and glueing two 0.1524 mm resin-insulated copper wires. Contacts consisted of the cut edge of the wire (0.018 mm 2 ) (Châtillon et al, 2011). Electrodes were implanted in the CA3 subfield of the ventral hippocampus (AP: −4.4, ML: ±4, DV: −8.8), medial entorhinal cortex (AP: −6.6, ML: ±4, DV: −8.8), ventral subiculum (AP: −6.8, ML: ±4, DV: −6) and dentate gyrus (AP: −4.4, ML: ±2.4, DV: 3.4).…”