In the Annals of Neurology, a team of physicians, led by Tony Ro of the Department of Psychology at Rice University in Houston, Texas, report the unusual case of a woman who began to feel sounds following a stroke
The woman, a 36-year-old professor, suffered a rare type of cerebrovascular accident: a lacunar infarct, in which a small blood vessel deep within the brain became blocked. This led to damage in the ventrolateral thalamic nucleus (VL) on the right side of her brain.
When first examined, some 9 months after her stroke, the woman reported significant changes in her sensations and attentional abilities. Her abilitiy to detect tactile sensations on her left foot, hand, arm and face were markedly decreased. She also reported hemispatial neglect - that is, she would occasionally bump into the left side of doorways and veer rightwards when driving.
About 1 year after her stroke, the physicians performed a series of behavioural tests on the woman. She was still neglecting the left side of her body, but also demonstrated a phenomenon called unisensory anti-extinction: when two identical visual or tactile stimuli were presented simultaneously, one to either side of her body, the woman reported that the stimulus on the left was significantly stronger. But only 50% and 73% of the tactile and sensory stimuli, respectively, were detected when presented alone to the left side.
The woman then underwent two different types of neuroimaging (functional magnetic resonance and diffusion tensor imaging; the former providing images of brain activity, the latter of white matter tracts that connect different parts of the brain). The scans showed a small area of damage to the right VL.
About one-and-a-half years after her stroke, the woman was no longer neglecting the left side of her body, but instead reported that she had begun to experience sound-touch synaesthesia. She would feel tingling sensations in her left hand and arm when she heard certain sounds, such as the voice of a particular radio presenter, and this was confirmed by further behavioural tests in which she was presented with auditory and/ or tactile stimuli.
More brain scans were then performed. The fMRI showed that the lesion was exactly the same size, and in the same location, as the previous scans. But the DTI data showed that there had been a marked reduction in the number of fibres connecting the thalamus and the cerebral cortex in the right hemisphere, and that the remaining connections were more disorganized than those on the left.
The team of physicians therefore believe that the changes in the patient's sensory perceptions could have occured as a result of anatomical and functional re-organization of the neural connections between the thalamus and the cortex. For example, conoections damaged as a result of the stroke may have strenghtened the connections between the auditory and somatosensory cortices, which would produce the sound-touch synaesthesia demonstrated by the patient.
The VL was believed to be involved in motor function, but this study provides some evidence that it also has sensory functions. It also supports the idea that other reported cases of acquired synaesthesia following brain damage are a result of cross-wiring between sensory modalities.
Ro, T., et al. (2007). Feeling sounds after a thalamic lesion. Ann. Neurol. doi: 10.1002/ana.21219.
I read this report with great interest. The idea that the brain is plastic is fascinating and old. One of the founders of the modern psychiatric research hospital, August Forel, wrote about this possibility already at the beginning of the last century.
The Nobel Prize laureates T. Wiesel and D. Hubel at Johns Hopkins University demonstrated in the visual system in ca. 1960 that the organization of the cerebral cortex (the piece of tissue on the surface of the brain that looks like a convoluted rind and seems to define us most profoundly) can be modified through experience during brain maturation. Ca. 1980, J. Kaas, M. Merzenich and colleagues at Vanderbilt University provided evidence that somatic sensory cortex where touch is processed can be modified even in the mature brain. These findings were ever more intriguing, because the nerve cells in the mature brain were thought not to proliferate anymore. Now we know that new neurons are produced in some regions of the adult brain, though at a very low rate.
With these discoveries in mind, researchers have looked for signs of brain plasticity with ever gaining momentum, trying to apply the concept in recovery from brain damage by injury and disease.
I may add a note of caution. Actual plasticity would stipulate that the brain is molded into a new wiring plan. The observation that one brain function may appear waxing while another one is waning does not necessarily entail such reorganization. The case reported at Rice University may be simply the result of the unmasking of a normally hidden function in multi-modal brain regions where the information from several senses is processed. That is, as one function wanes the other is left to take the stage. But it has been there at work all along veiled from our views perhaps by our own ignorance. Whether connections are truely strengthened, leading to novel brain organization remains to be demonstrated, and I hope that the findings at Rice University encourage more research in that direction.
Peter Melzer, Ph.D.,
Brain and Mind Institute,
I really really need help in understanding why nobody can do anything for my husband who suffered a bi-lateral and midbrain stroke on 1/26 in the ER and didn't get diagnosed until he was transferred to another hospital on 1/29. By then he was already in a coma but after almost 3 weeks he woke up. He was doing well and transferred out of the ICU after 48 days. As he improved he was again transferred to a rehab facility. Even though his memory and time telling were gone, he was improving slowly and can carry a conversation and joked. Then on 5/20 I was told he must have had a seizure after his therapy sessions. After that day, his speech was affected. His oncologist then decided to re-admit him back to the hospital for more tests to determine if perhaps his tumor came back. (He is a 61/2 years GBM survivor) PET scan, MRI/MRA and lumbar punctual all came back negative, but he stopped talking and because he is not responding as well as before, he was not given any solid food for fear of choking and is now being fed through tube feeding. What I don't understand is nobody can tell me what's going on with my husband and I am running out of resources to get him back to where he was before. He is still in the hospital because no rehab facility is willing to take him due to the fact that he is at a level that requires more work and couldn't communicate. I was told to put him in a nursing home. I cannot do that to him. He deserves more than that. I am so frustrated I could scream.. If you can help me with anything that could help my husband's condition, I appreciate it very much. Maybe there is some therapyor hospital/facility that can help him regain his speech and memory and his muscle.
Buy the book, Head Cases by Michael Paul Mason. Mason is a traumatic brain injury (TBI) case manager. He discusses the resources available to TBI patients in the first couple chapters.