Subdural porous and notched mini-grid electrodes for wireless intracranial electroencephalographic recordings

BACKGROUND: Intracranial electroencephalography (EEG) studies are widely used in the presurgical evaluation of drug-refractory patients with partial epilepsy. Because chronic implantation of intracranial electrodes carries a risk of infection, hemorrhage, and edema, it is best to limit the number of electrodes used without compromising the ability to localize the epileptogenic zone (EZ). There is always a risk that an intracranial study may fail to identify the EZ because of suboptimal coverage. We present a new subdural electrode design that will allow better sampling of suspected areas of epileptogenicity with lower risk to patients. METHOD: Impedance of the proposed electrodes was characterized in vitro using electrochemical impedance spectroscopy. The appearance of the novel electrodes on magnetic resonance imaging (MRI) was tested by placing the electrodes into a gel solution (0.9% NaCl with 14 g gelatin). In vivo neural recordings were performed in male Sprague Dawley rats. Performance comparisons were made using microelectrode recordings from rat cortex and subdural/depth recordings from epileptic patients. Histological examinations of rat brain after 3-week icEEG intracerebral electroencephalography (icEEG) recordings were performed. RESULTS: The in vitro results showed minimum impedances for optimum choice of pure gold materials for electrode contacts and wire. Different attributes of the new electrodes were identified on MRI. The results of in vivo recordings demonstrated signal stability, 50% noise reduction, and up to 6 dB signal-to-noise ratio (SNR) improvement as compared to commercial electrodes. The wireless icEEG recording system demonstrated on average a 2% normalized root-mean-square (RMS) deviation. Following the long-term icEEG recording, brain histological results showed no abnormal tissue reaction in the underlying cortex. CONCLUSION: The proposed subdural electrode system features attributes that could potentially translate into better icEEG recordings and allow sampling of large of areas of epileptogenicity at lower risk to patients. Further validation for use in humans is required

Latencies to behavioral generalized convulsion (GC) during hyperthermia at P10.

<p>Histograms showing that in the lesioned pups latency for GC is significantly shorter than in controls. This decrease is independent of gender and testosterone treatment (* = p<0.05, ** = p<0.01, *** = p<0.001).</p

Plasma corticosterone level (PCL) changes following treatments.

<p><b>A</b>) Histrograms showing changes in PCL before and after the cortical lesion in nmol/ml at P1 in males (top) and in females, bottom). <b>B</b>) Mean PCL variations for all the experimental groups in percentages. Note that the LM and LF+T groups were the only ones that showed an increase of corticosterone levels following cortical dysplasia induction at this age, whereas the others showed diminution. These increases were statistically different from their controls, notably LM compared to NM (*** p<0.001), LF+T compared to NF (* p<0.05) and to LF (** p<0.01).</p

Effect of testosterone on lesioned females.

<p><b>A</b>) Photographs showing the effects of testosterone treatment on female anatomy at P10. Male rat (NM, left), female rat (NF, middle) and testosterone injected female (F+T, right) are shown. Testosterone exposure during the fetal and perinatal periods altered the development of secondary sex characteristics in female rat (F+T) pups such as the presence of a longer anogenital distance (top) and the lack of breast (bottom). <b>B</b>) EEG in an adult LHSF+T rat showing an example of an electrographic seizure. Seizure activity recorded over a 60-second period from the right primary motor cortex (M1, top trace) and hippocampus (CA1, bottom trace) ipsilateral to the lesion. <b>C</b>) Pre-seizure baseline rhythm was composed of irregular, low amplitude, 6 to 12 Hz frequency activity. In this case, the first behavioral manifestation was characterized by abrupt rearing and hind limb myoclonus associated with the slow wave polyspiking pattern shown by the first arrow. Interictal epileptic spike or spike and wave activity was also recorded frequently throughout this period (arrows 2 and 3). <b>D</b>) Just before the seizure, the epileptic discharges were intermingled with a burst of hippocampal fast activity (1), followed by a slow rhythmic activity at a frequency of 1 to 3 Hz (2) progressing into 6 to 8 Hz rhythmic activity (3). <b>E</b>) During the seizure the EEG trace showed a prolongation of the rhythmic activity characterized by high amplitude oscillations equivalent to two to ten-fold of baseline rhythm at a lower frequency range (5–7 Hz range). <b>F</b>) The end of the seizure (1) is marked by low amplitude fast activity intermingled with periodic epileptic discharges before a progressive return to theta activity (2). The clinical manifestations included freezing followed by myoclonus, and abrupt rearing and falling. Acquisition frequency was 200 Hz, and filtering at 1–35 Hz. Horizontal bar = 1 second; vertical bar = 500 µV.</p

Photomicrographs of cresyl violet sections and Cavalieri's cortical lesion volumes estimations in the adult rats.

<p>In <b>A</b>), a confirmation example of the bipolar electrodes placement for EEG recordings in a LHSF+T rat is shown in motor cortex M1 (left panel) and in the <i>cornus ammonis</i> region one (CA1) of the hippocampus (right panel). <b>B</b>) Cresyl violet stained coronal section through the dysplasic lesion in sensorimotor cortex of P120 rat brains, male (left) and female (right), that received a freeze-induced lesion at P1 and hyperthermic seizure at P10 (LHS). Photomicrographs are showing a similar and well-formed, four-layered microgyrus in the middle of each panel for both genders. In <b>C</b>), (Top panel) histograms of the volume estimations in the LHSM versus LHSF groups using the Cavalieri's principle for the focal mycrogyrus (left) and total amount of altered neocortex (right). (Bottom panel) diagrams illustrating the region of interest for sampling in each case highlighted with grid points. All Scale bars = 250 µm.</p