Language plays a critical role in the development of the brain. As Patricia Kuhl demonstrated during Monday morning’s keynote session at CNS 2013, early childhood exposure to multiple languages not only enhances the ability to learn languages later in life, but also improves mental flexibility and creative thinking. But what can the way the brain handles language tell us about the inner workings of cognition and memory? Monday afternoon’s at CNS 2013 took a hard look at the link between memory and language, in everyone from healthy patients to those with schizophrenia and amnesia.
Tamara Swaab of the University of California, Davis, compared two methods the brain uses to glean meaning from language. In the first, the “good enough” route to comprehension, we surmise the gist of what’s being said, both from the words we hear and the situations in which we’re hearing them. The second method, the combinatorial processing network, allows for much more precise understanding of language. “Working memory may influence which of these routes you preferentially use,” Swaab told the audience. This type of memory is controlled by the dorsal lateral prefrontal cortex and is critical in providing the context from past experience necessary for the second method of comprehension to work.
Swaab hypothesized that a patient with schizophrenia, whose prefrontal cortex doesn’t work properly, would have trouble with this form of comprehension, and tests in reading comprehension bore this out. In fact, Swaab said that subjects with these deficits often relied heavily on the good-enough comprehension method, potentially allowing for the gaps that can lead to less-than-complete comprehension of a situation.
In her studies of the hippocampus in patients with amnesia, Melissa Duff of the University of Iowa explained how she and her colleagues have uncovered evidence for the role that declarative memory plays in language processing. Through trials asking subjects to describe intricate shapes on cards, the team found that subjects who have amnesia due to problems in the hippocampus improved with practice but weren’t able to demonstrate the same playfulness with language that healthy subjects could. Without the faculties of a working hippocampus, subjects with amnesia weren’t capable of the “rapid combination and recombination…to create novel ways of thinking,” Duff said.
Two of the symposium’s speakers discussed the costs and benefits associated with cognitive control of language processing. Sharon Thompson-Schill of the University of Pennsylvania described experiments in which research subjects were presented with an object, such as a wooden chair. But instead of being asked simply to identify the object or its most common function, they were asked to articulate a novel use for the chair – say, as firewood. At the same time, Thompson-Schill and her colleagues excited and suppressed different parts of the prefrontal cortex with electrodes.
To simply identify the chair, the prefrontal cortex would helpfully strain out unneeded information to reach an answer. But, in this more complicated situation, Thompson-Schill explained that you would “be better off not to suppress all of the information that’s normally irrelevant.” She added that this process demonstrated a benefit of cognitive language processing. However, if the prefrontal cortex suppresses that typically irrelevant information, people could see a loss of creativity and the failure to complete this task.