I have a confession to make: I haven’t read Daniel Dennett’s Consciousness Explained (I am reading Dennett’s Brainstorm and so far I’m enjoying it). So, I’m not exactly in a position to argue against Dennett’s Consciousness Explained. However, I think there is a plausible evidence against one of Dennett’s argument. Let’s begin with Dennett’s argument. Dennett argues against what he calls “Cartesian Materialism“, which is the view there is a central region that integrates all conscious experience. One of Dennett’s argument against Cartesian Materialism is that neuroscientists discount it given the overwhelming evidence that different conscious experience is stored at different areas of the brain. For example, visual experience happens in the visual cortex, but there’s no the center of consciousness that stores that experience. Dennett might be correct that there is no central region of the brain for consciousness, but there is recent evidence that appears to contradict his claim.
The evidence I’m referring to is one that appears in recent news. In one news outlet Business Insider, it reports that neuroscientists may have found some region in the brain that they can “switch” on or off. Specifically, neuroscientists from George Washington University were experimenting with an epileptic patient by switching off her consciousness (and then switching it back on). A few years before this experiment, Francis Crick and Christof Koch proposed a hypothesis that the region of the brain known as the Claustrum is the center of consciousness that integrates different informational inputs. In the experiment, neuroscientists place an electrode between Claustrum and anterior-dorsal insula. When they stimulated an electrode, the patient lost consciousness. The experimental result indicates that the Claustrum could be the center of consciousness, which supports Koch and Crick’s hypothesis. I think their hypothesis is a version of Cartesian Materialism. If their hypothesis is supported by recent evidence, then there is evidence for Cartesian Materialism. This could mean that Dennett was wrong that there is no center of consciousness. So, does this mean that Cartesian Materialism is vindicated from Dennett’s critique? Probably not.
While the experimental result is interesting, it is only a single case study that hardly qualifies as a sufficient representative sample. Moreover, there needs to be an experiment that accounts for both epileptic and non-epileptic patients to ensure that this isn’t a unique case for an epileptic patient (unless there is an ethical issue with that kind of experiment). Nonetheless, one could reasonably expect that the same thing that happens for an epileptic patient could happen if one places an electrode in the same region for non-epileptic patients and then stimulates it.
Another thing to consider is that there is another experiment four years ago that suggests an alternative hypothesis that isn’t committed to Cartesian Materialism: the Claustrum consists of distinct “zones” with “unimodal” neurons that respond to specific kind of sensory inputs. The visual “zone” consists of neurons that respond to the visual stimuli, but not the auditory stimuli. Likewise, the auditory “zone” consists of neurons that respond to auditory stimuli, but not visual stimuli. In other words, the auditory and visual experience may not be integrated in one conscious experience, but rather they remain isolated from each other in different “zones” of the Claustrum. So far, there has been an experiment with primates as test subjects that produces a result that supports the alternative hypothesis. Given that both homo sapiens and their close cousins share a common ancestry, it is not unreasonable to think that their Claustrum has similar functions. One could infer that if our close cousins’ Claustrum does not integrate multiple sensory information, then likewise our Claustrum may not be the center of consciousness (there is another evidence that the function of Rats’ Claustrum is an interhemispheric coordination of whisker representations from both the somatosensory and motor cortical areas. So, the function of the Claustrum may not necessarily have to be the center of consciousness for all non-human animals). It could be the case that the experimental result from the epileptic patient could support the alternative hypothesis. Perhaps all zones of the Claustrum were turned off simultaneously by an electrode. Consequently, the evidence is underdetermined between two available hypothesis. So far, it appears that Cartesian Materialism is not vindicated, but it is also not ruled out.