Electrical stimulation of the human claustrum

Annotations for: Electrical stimulation of the human claustrum

✅ Key Points

This is key point about the Koubeissi (2014) paper. If you increase the current so much then the electrical current and the area of the brain that you are stimulating increases. [@bickelElectricalStimulationHuman2019, p. 298]

Increasing stimulation current leads to larger electrical fields affecting a relatively large area of the brain (up until ~36.5 mm2) and increases the probability of nonspecific perturbation of adjacent areas of the brain beyond the targeted pool of neurons [13] [@bickelElectricalStimulationHuman2019, p. 298]

Background

The claustrum is a thin, elongated band of gray matter surrounded by thick bundles of white matter in the proximity of basal ganglia and insula [@bickelElectricalStimulationHuman2019, p. 296]

While much is known about the claustrum’s anatomy, its function remains mysterious and is subject to hotly debated discussions and even dedicated societies (e.g., Society for Claustrum Research) [@bickelElectricalStimulationHuman2019, p. 296]

Hypothesis

In the present study, we tested if awareness could be impaired with unilateral and bilateral stimulations directly applied within the claustrum in 5 subjects. [@bickelElectricalStimulationHuman2019, p. 296]

Methods

5 Participants in the sample with medication-resistant epilepsy [@bickelElectricalStimulationHuman2019, p. 296]

5 patients (3 females) with pharmacologically resistant epilepsy undergoing invasive electrophysiological monitoring [@bickelElectricalStimulationHuman2019, p. 296]

Electrodes implanted, presumably close the site of where the epileptic electrical activity occurs from [@bickelElectricalStimulationHuman2019, p. 296]

Subjects in this study had electrodes implanted in multiple regions of their brain including targets within the insula [@bickelElectricalStimulationHuman2019, p. 296]

Used routine electrical brain stimulation methods. Nothing crazy here. [@bickelElectricalStimulationHuman2019, p. 298]

For this study, we used EBS parameters that are routinely used in such clinical mapping procedures with a S12X Grass cortical stimulator [@bickelElectricalStimulationHuman2019, p. 298]

The current was considered to be in a more normal range for electrical brain stimulation studies unlike that of Koubeissi (2014) [@bickelElectricalStimulationHuman2019, p. 298]

charge-balanced alternating square-wave pulses with 0.2 to 0.3 ms width per phase, at 50 Hz, with stimulation amplitudes between 2 and 10 mA [@bickelElectricalStimulationHuman2019, p. 298]

Results

claustral contact referenced to 1 cm dorsal contact (in the vicinity of the white matter) caused a loss of muscle tone in the right arm and leg and an arrest of tongue movements at 6 mA stimulation most likely due to involvement of the adjacent corticospinal tracts [@bickelElectricalStimulationHuman2019, p. 298]

subject 1, fully aware and no loss of consciousness only loss of muscle tone [@bickelElectricalStimulationHuman2019, p. 298]

patient was fully aware of these effects and denied changes in her thoughts or emotions [@bickelElectricalStimulationHuman2019, p. 298]

“strange” sensations in the face down to leg [@bickelElectricalStimulationHuman2019, p. 298]

claustral contacts at 4 mA and 6 mA caused a “strange” skin sensation from the face running down the leg [@bickelElectricalStimulationHuman2019, p. 298]

subject 2 - no loss of consciousness reported [@bickelElectricalStimulationHuman2019, p. 298]

the patient denied having loss of awareness and stated that she was aware of objects and people around the bed. [@bickelElectricalStimulationHuman2019, p. 298]

4 of the 56 implanted electrode contacts were located in the left claustrum. [@bickelElectricalStimulationHuman2019, p. 302]

stimulating the most ventral parts of the claustrum (up to 6 mA), the patient experienced an aura of anxiety [@bickelElectricalStimulationHuman2019, p. 302]

adjacent dorsal stimulations up to 2 mA caused hot flashes, and stronger stimulations could not be applied. [@bickelElectricalStimulationHuman2019, p. 302]

subject 3 - Harder to say the numbers, no loss of consciousness. Perhaps harder to say the numbers due to anxiety and hot flashes [@bickelElectricalStimulationHuman2019, p. 302]

behavior of clenching her fist and counting back continued uninterrupted but she felt it was hard to say the numbers [@bickelElectricalStimulationHuman2019, p. 302]

subject 4 - No changes to awareness [@bickelElectricalStimulationHuman2019, p. 302]

Bilateral stimulation up to 6 mA did not have any subjective or objective effects [@bickelElectricalStimulationHuman2019, p. 302]

the patient felt the urge to lift the right leg, and at 9 mA, the leg jerked during stimulation [@bickelElectricalStimulationHuman2019, p. 302]

Subject 4 - no loss of consciousness. Some jerking in the lef [@bickelElectricalStimulationHuman2019, p. 302]

Again, the subject was probed directly, and she denied any change in her awareness of the situation and of her surroundings. [@bickelElectricalStimulationHuman2019, p. 302]

bilateral stimulations, the patient experienced an unpleasant acid-like sensation in the throat with currents at 1–2 mA, but did not experience a change in awareness. [@bickelElectricalStimulationHuman2019, p. 302]

Subject 5 - some sensations in the mouth but no loss of consciousness reported [@bickelElectricalStimulationHuman2019, p. 302]

stimulating more dorsal electrodes, he experienced a jabbing/burning pain in the mouth at 2 mA. Stronger stimulations could not be applied [@bickelElectricalStimulationHuman2019, p. 302]

Conclusions

Stimulating the claustrum only caused some sensorymotor effects [@bickelElectricalStimulationHuman2019, p. 302]

Stimulations mainly caused sensory-motor effects ranging from acute loss of tone in the contralateral limbs; sensation of numbness and warmth on the contralateral arm; urge to lift the right leg with bilateral stimulation; or arrest of tapping movement. [@bickelElectricalStimulationHuman2019, p. 302]

In comparison to the Koubeissi (2014) study. The differences may be explained because Koubeissi stimulated the extreme capsule and not directly the claustrum [@bickelElectricalStimulationHuman2019, p. 303]

We stimulated the claustrum directly while their observations were attributed to the stimulation of the claustrum even though the actual electrical charge was delivered in the extreme capsule, between the anterior insula and the claustrum [@bickelElectricalStimulationHuman2019, p. 303]

In comparison to the Koubeissi (2014) study. [@bickelElectricalStimulationHuman2019, p. 303]

Most stimulated locations in our report were more posterior and inferior compared with their stimulated location, [@bickelElectricalStimulationHuman2019, p. 303]

In comparison to the Koubeissi (2014) study, which used higher currents and for longer durations [@bickelElectricalStimulationHuman2019, p. 303]

Most of the maximal currents used in our study were lower compared with their study, but in one patient, we used a comparable peak current and current density (Subject 2, 0.3 ms/ phase, 10 mA), however, only for 1 s, while Koubeissi et al. stimulated for 3 to 5 s [@bickelElectricalStimulationHuman2019, p. 303]

Implications

Results are only a glimpse into EBS of the claustrum. But put the Koubeissi studies results into question [@bickelElectricalStimulationHuman2019, p. 303]

mindful that our bedside clinical electrical stimulation procedures only provide a short glimpse to the immediate effects of electrical charge delivery to the claustrum [@bickelElectricalStimulationHuman2019, p. 303]

They don’t rule out that the claustrum might be important in consciousness but that perhaps conscious experience involves multiple areas of the brain working together? [@bickelElectricalStimulationHuman2019, p. 303]

We are fully aware that our failure of inducing loss of awareness with electrical stimulation of the claustrum does not necessarily mean that the claustrum is not important for human consciousness or subjective awareness. [@bickelElectricalStimulationHuman2019, p. 303]

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