A more than busy time here on the farm even as I see some interesting news about which to post. I hope to catch up and have the time and energy to blog about some of these. So today, I write about the curious claustrum which I have read little about before this past week when a report came up about its role in consciousness. Some brain insights come from clinical work helping people cope with severe epilepsy such as Sperry et al’s split brain research or Brenda Milner’s work on memory with H.M. after his hippocampectomy. These surgeries help to control the spread of the epileptic storm that originates and spreads from a particular locus, often in the temporal lobe. As a part of surgery they stimulate parts of the patient’s brain as they try to excise the damaged part but preserve as much function as possible. A recent effort in this regard placed an electrode next to the claustrum, a small band of neurons with at least many cortical connections to perceptual and motor areas. It is situated between the midbrain’s basal ganglia and the temporal lobe’s cortex.
We have known about the existence of this structure for at least a century. The great Spanish neuroanatomist Ramon y Cajal documented it early in the 20th Century. Anyway, when they turned the electrode on, thereby shutting down the claustrum, the patient remained awake but seemed unconscious. The frontal lobe EEG became more synchronized which is a sign of non-specific processing, even resting. When the electrode was turned off, the patient regained consciousness but had no memory of the episode. They also had the patient begin repeating a word before stimulus onset and found that the patient would keep repeating the word for awhile but then his or her speech began to fade in loudness and articulation. The scientist-practitioners here interpreted this as suggesting that the claustrum is involved in initiating/instigating consciousness.
And this has been hypothesized before based upon more general knowledge by Francis Crick (of DNA fame) and Christof Koch as they conceptualized the function of the claustrum as the conductor of an orchestra, helping the different parts to play together in the creation of consciousness. So this clinical finding fits that hypothesis. Now,of course, the cautions are several. First, this patient did not have a normal, healthy brain and had already had part of the hippocampus removed. More importantly modern anatomical studies across some presumably sentient and conscious species, including cetaceans, have found a quite variable structure inter-species and even within a species the claustrum appears to be not so much an integrated and integrative structure but a series of neuron clusters which may or may not process as a “conductor.” An easy structure to see but hard to study and understand.
The clinical study reminded me of a dissociative phenomena called highway hypnosis. That is when a driver drives down the highway in an automatic, unconscious fashion, clearly negotiating the task, only to ‘wake up’ from the trance down the road and realize he or she has no memory of the trip or the experience during that time. This is thought of as a ‘normal’ dissociative event, awake but not conscious, like the patient in this study. And this reinforced for me the difference between the two, awake and conscious, and their possible permutations. We can be awake but unconscious as in highway hypnosis (or even regular hypnosis), not awake but conscious as in dreaming, not awake and not conscious as in deep sleep, and awake and conscious as I am now (and you too, I hope).
Finishing up, some debate the origin (embryologically) of the claustrum: is it midbrain and basal ganglia or cortical? Its placement is right between the two. Its known connections are cortical, however, and its subcortical connections uncertain at best. It has not been found consistently in some species that are presumed, rather clearly I think, to be conscious, so if it is the conductor in humans, how do these other animals manage? My bias is that any key to consciousness lies in some synergy among areas and not so localized and that the integration between cortical and lower structures is essential.
So more curious questions again, and I like it.