In a study by Koubeissi et al. (2014) there was an experiment on a patient to find out which part of the brain caused her epilepsy. In this experiment they have found out that if they electrically stimulate her left claustrum, the person would lose consciousness.

My question is: If they have stimulated her right claustrum, would that caused her a loss of consciousness as well? In other words: Are both claustrums necessary for a conciousness to appear in an ordinary healthy human brain?

Koubeissi, M. Z., Bartolomei, F., Beltagy, A., & Picard, F. (2014). Electrical stimulation of a small brain area reversibly disrupts consciousness. Epilepsy & Behavior, 37, 32-35.


1 Answer 1


It's probably a bit more complicated than that. Cortical areas tend to be highly connected with their contralateral counterparts, so it's not really fair to expect that the effects of stimulation on one side of the brain doesn't impact the contralateral side.

The claustrum is itself a small gray matter region, but it is surrounded by white matter as well. Koubeissi et al used a fairly strong stimulus when they saw effects on consciousness; I have a hard time believing this stimulation was only affecting the claustrum and not fibers of passage at that stimulation intensity.

A recent study of 5 epilepsy patients attempted to replicate the Koubeissi finding, stimulating the claustrum (bilaterally in 4/5) in epilepsy patients, but none of the patients lost consciousness despite experiencing other effects. The authors suggest that the results presented in the earlier case study could be based on the unique circumstances of that patient, which include their epilepsy history and prior resection, and that the stimulation location in that Koubeissi case was not really directly in the claustrum. Additionally, Bickel & Parvizi were unable to use a stimulus as strong as the prior case report because their patients experienced negative side effects like painful muscle responses that Koubeissi did not see.

Bickel, S., & Parvizi, J. (2019). Electrical stimulation of the human claustrum. Epilepsy & Behavior.

Damasio et al, 2013 is another case study, where the patient had bilateral damage to a substantial portion of the brain, including the claustrum bilaterally. This patient had quite a bit of impact to various functions due to this damage, but they were still conscious. Therefore the answer to "Are both claustrums necessary for a conciousness" seems to be "no"; in a healthy brain it's a bit harder to say, because it's not ethical to damage the claustrum in healthy brains.

Damasio, A., Damasio, H. & Tranel, D. Persistence of feelings and sentience after bilateral damage of the insula. Cereb. Cortex 23, 833–846 (2013).

There are also other papers showing suppression or recovery of consciousness through stimulation of other brain regions besides the claustrum.

Redinbaugh, M. J., Phillips, J. M., Kambi, N. A., Mohanta, S., Andryk, S., Dooley, G. L., ... & Saalmann, Y. B. (2019). Central thalamus modulates consciousness by controlling layer-specific cortical interactions. bioRxiv, 776591.

Schiff, N. D., Giacino, J. T., Kalmar, K., Victor, J. D., Baker, K., Gerber, M., ... & Farris, S. (2007). Behavioural improvements with thalamic stimulation after severe traumatic brain injury. Nature, 448(7153), 600-603.

  • $\begingroup$ Keep in mind that Koubeissi et al (2014) emphasized that stimulation of the target area at lower current (6 ma) did not disturb consciousness, but at 14 ma it did, so as you mention, Bickel, S., & Parvizi, J. (2019) having used lower current (I did not read their paper since it is behind a pay wall), can not rule out the role Koubeissi discovered. $\endgroup$ Mar 9, 2021 at 16:45
  • $\begingroup$ @DaltonBentley It's a general principle in stimulation experiments that stronger stimuli are most likely to have "off-target" effects. I'd agree that Bickel does not demonstrate that Koubeissi's findings are not possible with stimulation targeting the claustrum, but I'd say they raise strong doubts that the claustrum was actually the Koubeissi target. Certainly enough doubt to take Koubeissi's result as fairly weak evidence. $\endgroup$
    – Bryan Krause
    Mar 9, 2021 at 16:49
  • $\begingroup$ As Koubeissi notes though, the LOC reversed immediately upon termination of the stimulus, in contrast to afterdischarges or seizures in other regions resulting from a high current. I read a 2019 article yesterday (DOI: 10.1002/hbm.24892) studying LOC in Viet Nam head trauma patients which mapped networks (instead of voxel local sites) to brainstem LOC causing areas, suggested peak in bilateral claustrum (good luck reading it---was put in anticorrelation terms and ambiguous language at times). $\endgroup$ Mar 10, 2021 at 15:20
  • $\begingroup$ @Dalton The issue isn't whether the stimulus is causing the effect seen, but whether it's specifically stimulating the claustrum or some fibers of passage, since the claustrum sits right among those. $\endgroup$
    – Bryan Krause
    Mar 10, 2021 at 15:37
  • $\begingroup$ I recall the complaint of a retired CEO acquaintance to me that he didn't use the Internet because "everything is connected to everything." Also a lot of interindividual variability in locations. interesting that stimulating cat claustrums caused them to become unresponsive also, mammalian brains having fairly common features (see Feinberg and Mallatt 2013 for suggestion consciousness had origin in Cambrian and has genetic basis). $\endgroup$ Mar 12, 2021 at 15:30

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