When it comes to the “right brain vs. left brain” discussion, neuroimaging research has shown us just how communicative the hemispheres of our brain actually are. Unless the connection between them is physically severed, information zips across the hemispheres during the vast majority of tasks that our brains accomplish every second.
Broca and Wernike
As far back as the 19th century, European physicians Paul Broca and Carl Wernicke noticed that their patients, who had circumscribed lesions in the left hemisphere, showed a peculiar symptom profile. Broca’s patient was nicknamed Tan because that was one of the very few words that he could say, and he seemed to have little trouble understanding speech but had great difficulty producing it.
Learn more: Language and the Brain
By contrast, Wernicke’s patients, whose brain damage was just a little bit below the area where Tan’s was, were able to produce speech, but when they did, it sounded like word salad—gibberish. They had trouble with speech comprehension, whether it was understanding what someone else was saying, or saying something themselves.
Dominant Hemispheres, Dominant Hands
Studying such groups of lesion patients, then, helped neuroscientists discover that certain cognitive functions like language are localized primarily to one side. This assignment of different functions to the two different hemispheres is known as lateralization. When it comes to our senses and actions in particular, the two sides of the brain do process different sets of information.
The left side of space is represented primarily in the right hemisphere, and vice versa. This means that your right hand is controlled by the left side of your brain and what you see in your left visual field is projected to the back of the right side of your cerebral cortex. It’s this fact that I’ve heard some acting coaches use to justify a technique designed to make a person more creative. Engage the left side of your body, they say, and you’ll tap into your creative right brain. But there are a few assumptions that such an explanation glosses over, most of which aren’t true.
Just like you have a dominant hand, most likely you also have a dominant hemisphere—or, I should say, because you have a dominant hemisphere, you also have a dominant hand. Neuroscientists are still working out the details of how related the lateralization of cognition and handedness really might be and how they develop, and the story is getting more complicated by the day.
Learn more: Are Creative People Right-Brained?
But for most of us who are right-handed, our left hemisphere is our dominant hemisphere, and the left side of our brain contains most of our language function.
And people sometimes point to left-handed individuals, claiming that they’re more likely to be engaged in creative careers than right-handed ones, and that surely must be because they’re dominated by their right hemisphere. But if you’re left-handed, then there’s only about a 20% chance that your right hemisphere is your dominant hemisphere. And there’s also a 20% chance that both of your hemispheres contain language function.
As for the rest of the lefties, they’ve still got about a 50%–60% chance that most of their language function is on the left side. So already, as you can see, even for language, arguably the star of lateralization, the story isn’t quite as neat as we would like it to be.
The Brain and Language
And even though many language functions rely on an intact left hemisphere, as Broca and Wernicke noted, the right hemisphere certainly participates in verbal communication. The right side is much better at deciphering prosody and accentuation, while the left is the home of the grammar police and the dictionary.
For example, in both sets of patients, the physicians and their colleagues noticed that some aspects of speech were relatively preserved. Prosody, for example—the music of speech—seemed to be retained. In other words, their speech contained the appropriate ups and downs of conversation; you could hear the emotional intent in the melody of their speech.
Learn more: Arousing Expectations: Melody and Harmony
But patients with right hemisphere damage can show deficits in prosody; they have trouble distinguishing and expressing modulations in speech. Aha, you might say. If there ever was an artistic side to language, surely it would be prosody. But I suspect that many a great writer might take issue with that stance. So, what else does the right hemisphere do that the left does not? And how do we know?
Left and Right Brain Roles
Tracking activity in the brains of healthy people while they’re engaging in different tasks, as we do with neuroimaging, provides another, perhaps more modern window into laterality. For example, neuroimaging studies suggest that the two hemispheres might play different roles in emotion processing, with the left hemisphere showing somewhat greater activation for happy or positive emotions and the right hemisphere showing more activity during negative emotional processing.
One particularly interesting insight that neuroimaging has given us is the finding that white matter tracts, or the wiring diagram of the two hemispheres, is different. The wiring of the right hemisphere has been called more efficient because it has greater connectivity between regions.
Think of a city with a really good subway system, like Manhattan, making it easy to get from one side of the city to another. The left hemisphere, in contrast, seems to be more modular. It’s more like a cluster of little cities operating more independently, like Los Angeles, where every mini-city has its own municipal transport system and the cities themselves are not well connected. Santa Monica and Beverly Hills have different governing bodies, so it’s hard to get from one to the other using public transportation.
Learn more: How Your Brain Works
Left and Right Brain Communications
It’s this wiring difference that might explain why the left hemisphere seems to contain regions that operate somewhat more independently and are more specialized than the regions in the right hemisphere, which are involved in more integrative processes like visuospatial tasks—recognizing faces, for example, or arranging a set of blocks to match a pattern, or paying attention to all of space, not just one side of it.
So it’s easier to find specialization in the left than the right hemisphere. And here, too, people looking for evidence for the association between the right brain and creativity and the left brain and logic point to these wiring differences. If the right brain is more interconnected, does that make it easier for it to generate new ideas, finding new connections between remotely associated concepts?
Not so fast. Neuroimaging research has also shown us just how communicative the two hemispheres are. Unless that connection between them is physically severed, information is zipping across the hemispheres during the vast majority of tasks that we ask our brains to accomplish.
And in many regions, signals pass from one hemisphere to the other more quickly than they do within a single hemisphere—that is, some signals from the left and right prefrontal cortex can be exchanged more efficiently than signals from the back to the front of the brain in the same hemisphere.