Losing half a brain, and other stories

Last week I had the pleasure of attending the meeting of the British Association for Cognitive Neuroscience. As well as the impressive selection of cake during teabreaks, the conference featured a steady trickle of tidbits and tasters of cutting edge research, in London and beyond. Two of the most striking talks were on the subject of plasticity, both neural and mental.

First up, Dr. Frederique Liegois gave us a stunning reminder of the gross scale plasticity in early childhood. She reported on the mental and linguistic faculties of children who have undergone drastic but necessary removal of a whole cerebral hemisphere to prevent recurrent epileptic seizures. These children literally have lost half their brain. The talk emphasised what we can learn from such neuropsychological cases, in terms of adverse effects on linguistic and cognitive development. While differences exist, Liegois' data suggest the benefits of the operation outweigh its drawbacks. And this is truly staggering. Because on several measures, intellectual development proceeds close to normal, and in some cases the right hemisphere picks up the linguistic slack from the dominant left hemisphere. Speech is often close-to-normal, with only slightly altered lilt and pronunciation. All with only half a brain. It makes you wonder about the benefits of having two, symmetrical hemispheres. Like having two eyes, it offers redundancy in the case of injury. But surely the energy needed to run both sides of the brain is too much of an evolutionary cost to make this the only reason?

Second, Dr. Katerina Fotopoulou reminded us that just like the brain, the mind is plastic. In a recent issue of Neuropsychologia, Fotopoulou and colleagues report a fascinating case of recovery from anosognosia. Anosognosia (Greek - without knowledge) is the term given to a lack of awareness or insight into a particular neurological condition. In extreme forms, anosognosia can result in very bizarre symptoms, such as in Anton's syndrome where cortically blind patients claim vigorously that they are able to see. Dr. Fotopoulou's patient was a 67 year old lady who had hemiplegia - paralysis of half of the body following a right-hemisphere stroke. However, she claimed to be able to move her arm, and breezily asserted that she could clap her hands. This was until Dr. Fotopoulou showed her a video of herself being examined:

"As soon as the video stopped, LM immediately and spontaneously commented: “I have not been very realistic”. Examiner (AF): “What do you mean?” LM: “I have not been realistic about my left-side not being able to move at all”. AF: What do you think now?” “I cannot move at all”. AF:“What made you change your mind?” LM: “The video. I did not realize I looked like this”."

This sudden onset of self-awareness was still present 6 months later. It appeared that allowing the patient a third-person perspective on herself had "cured" her anosognosia, and induced changes in the representation of her own body. While this is a single case report, and may not be representative, the data are tantalising. In particular, they suggest that onset of self-awareness can be sudden and transformative. This makes sense - we all have experienced the sudden "aha" moment accompanying retrieval of the name of that actor that you couldn't drum up during dinner the previous evening. Changes in awareness of the self may share similarities with other change in other aspects of consciousness, such as semantic knowledge, appearing from a first-person perspective as being all-or-nothing. Whether this mental plasticity is accompanied by some rapid form of neural reorganisation, or only a "change in the software", remains an open question.

Fotopoulou et al. (2009), “Self-observation reinstates motor awareness in anosognosia for hemiplegia, Neuropsychologia 47, 5: 1256-1260.