When a woman who had experienced a blockage of the blood supply to the right portion of her thalamus came to the attention of a group of researchers, they were intrigued. The thalamus is recognized as a key relay for sensory information en route to the cerebral cortex, yet few opportunities exist for exploring this midbrain structure’s role. What, the researchers wondered, might a stroke to one of its two lobes reveal about thalamic function?
To investigate this question, the international team of researchers engaged the woman in a six-year study. The team monitored her behavioral responses to light, tones, and mild electrical stimuli as well as her sensory responses to such stimuli using a connectional imaging technique developed by team member Van Wedeen, an HMS associate professor of radiology at Massachusetts General Hospital. Midway through the study, something extraordinary surfaced: The woman reported that she could feel sound.
Unlike, say, visual–visual synesthetes, who see letters of the alphabet as particular colors, people with sound–touch synthesia are exceedingly rare. Yet the woman was adamant: An array of sounds, including the voice of a radio announcer, elicited a skin tingling on her left side, the one affected by the blockage.
The woman’s brain showed that the neural pathways between the damaged portion of her thalamus and her cortex had become disorganized and diffused, while pathways between the companion lobe and the cortex remained robust. Such restructuring suggests that sensory pathways to the cortex may dynamically remodel after being damaged, reflecting the brain’s remarkable ability to compensate for injury.