The circuit diagram for the electrolytic lesioning device. An op-amp is used in a negative feedback loop to maintain a constant current through the two electrodes in the brain (RL). The op-amp was implemented as suggested by its accompanying evaluation kit and supplied components. The system is powered by a 12V power supply, and a boost converter is used to create a VCC and -VCC of 450V and -450V, respectively. The current through RL can be set by changing the resistance of the potentiometer, RS. ZP is a hypothesized physiological parasitic component, which could be either resistive or capacitive (dashed box).

a) Ex vivo demonstration of the electrolytic lesion technique in unfixed sheep cerebral cortex using an intracortical Utah microelectrode array. Sustained delivery of 250µA of direct current for 10 minutes between adjacent electrodes (400µm spacing) resulted in a clean spheroidal cavitation in cortex approximately 1.5mm in diameter. Ruler is marked every 500µm. b) Hematoxylin and eosin (H&E) stained slice of the lesion in (a) clearly shows the lesioned region. Arrows indicate tissue fold artifacts that resulted from the histology process, not the lesion. The other dark pink areas surrounding the cavitation in cortex are regions of necrosis. c) A smaller ex vivo lesion in unfixed cerebral cortex of another sheep created by decreasing the direct current amplitude and duration to 180µA for one minute. The cavitation has a diameter slightly over 0.5mm.

a) H&E stained slice from an in vivo demonstration of the lesioning technique in pig cerebral cortex. 150µA direct current passed through two adjacent electrodes (400µm spacing) for one minute resulted in a conical region of damaged parenchyma. The top of the conical region shows a line of damage which may be caused by physical removal of the microelectrode array after testing. Anatomically observed alterations are clearly demarcated, emphasizing the fine localization of the lesioning method. b) Region of intermixed necrotic and histologically normal neurons within the conical zone of damage is visible in a close-up of the slice from (a). Necrotic neurons have shrunken cell bodies. The microelectrode array is expected to continue recording from remaining healthy neurons after performing a lesion. c) Region of viable neurons outside the conical region of damage is visible in a close-up of the slice from (a). This shows the precise spread of the method, with intact, viable tissue present just outside the lesioned area.

Voltage traces from seven representative lesions in an awake-behaving rhesus macaque (Monkey H). Lesions are shown in chronological order and are labeled with an experimental ID in the form SYYMMDD, where S indicates the animal, followed by the date. Discontinuity at the beginning of the traces indicates transient voltages that were too rapid to be captured by the voltmeter, lasting between 0.13 and 0.33s. Traces only capture the voltage while the lesioning device was turned on (45 seconds for most lesions and 50 seconds for lesion H200120).

a) A representative comparison of recorded action potential waveforms, before and after the sixth and eleventh lesions (top, Monkey H; bottom, Monkey U). The location of the lesion electrodes on the arrays’ spatial layout are marked by black dots. Good quality signal was observed in the recording sessions immediately before and after lesioning (left, right). An action potential detection rate was determined from periods of task engagement (gray-scale shading, capped at 15Hz for visualization). b) As a proxy for neuron loss, a relative turnover in daily recorded neurons was determined by pairwise comparisons of action potential waveforms within three groups: pre-lesion days (pre-pre), pre-lesion versus post-lesion days (pre-post; up to three days post-lesion), and post-lesion days (post-post; four to nine days after a lesion). An inter-quartile range is shaded in grey for the set of 10 consecutive days leading up to lesion 11, the first in Monkey U. The median from this healthy control group was subtracted from all other pairwise comparisons to directly quantify a change in turnover. This pre-lesion group was then combined with the other pre-pre comparisons and tested against the pre-post and post-post groups. The change in the percentage of matching neurons dropped significantly after a lesion (Median test; * < 0.003, ** < 0.0003, corresponding to corrected significance levels of 0.01 and 0.001 for the three comparisons). Note, lesions 11-14 in Monkey U were well-spaced out over three months and considered as independent samples.

Connection diagram of the experimental setup for creating electrolytic lesions.

Lesion parameters used for ex vivo testing. Voltage was monitored with a voltmeter during lesioning, and notes were collected about the voltage. Tests that were performed solely to understand the effect of impacting and removing the microelectrode array without passing any current to create an electrolytic lesion are indicated with N/A for the current value. One ex vivo brain was used for all testing on 180702, and two ex vivo brains were used on each of the other two dates.

Lesion parameters used for in vivo testing. Voltage was monitored with a voltmeter during lesioning, and notes were collected about the voltage. Tests that were performed solely to understand the effect of impacting and removing the microelectrode array without passing any current to create an electrolytic lesion are indicated with N/A for the current value. One animal was used for all testing on a given date.