Researchers at Columbia University and Washington University have found that key parts of the human brain network that give a person the power to control and redirect their attention, a core cognitive ability that may be unique to humans. The team state that the new study suggests that the network may have evolved in response to increasingly complex social cues. The study is published in the journal Proceedings of the National Academy of Sciences.
Previous studies show that the human brain is powerful, however, even it cannot make sense of the entire sum of stimuli that bombards the person’s senses. Instead, it selects and prioritizes information based on what is needed at any given moment, this is called attention. And while attention is a fundamental characteristic of human cognition, and something that humans use all the time, the underlying brain circuits that give a person this ability remain largely unclear.
In order to better understand these circuits, the team compared the brains of primate and human subjects during a specific attention-seeking task. In so doing, they uncovered key clues about these so-called ‘attention networks’. The also found out how they evolved and how they underlie human cognitive abilities, and are already using this information to test what role they may play in psychiatric disorders.
The current study showed that in the human brain, there are two main attention networks, the dorsal attention network (DAN) and ventral attention network (VAN). The DAN is in charge of directing a person’s attention to something specific, and when it’s active, the VAN is silent. The data findings show that this keeps the person focused and limits their distraction. The results show that if a person sees something that is new, unique, or behaviourally relevant, the VAN will switch on. The researchers state that this give-and-take between the DAN and VAN allows humans to reorient their attention to what is most important.
In a series of experiments, using a primate model and later with human subjects, the researchers used functional magnetic resonance imaging (fMRI) to map brain activity. Before the start of a session, the subject memorized a specific target object. During the session, a stream of images appeared on various parts of a screen. The subject pushed a button when the target object appeared on the screen. fMRI technology allowed the researchers to see when various parts of the brain ‘switched on’ while the subject performed the task.
The fMRI results showed striking differences between the two species. The team were giving both the human and primate subjects the exact same task, their brain activity should have been more similar. That’s when the lab realized there was something else going on. First, they realized that the VAN, located in the right hemisphere of the human brain, had no equivalent in the primate brain. They also noticed the DAN had expanded in the human subjects, and observed enhanced cross talk between the human subjects’ brain hemispheres.
Taken together, these findings suggests that at some point in human evolutionary history, they evolved an additional attention network, perhaps in order to better process the world around them. The team explain that the human social world is far more complex than any of their primate relatives. It is possible this network evolved to help humans understand increasingly complex social cues, such as the subtle twitch of an eyebrow, or a shift in gaze, state the researchers.
Armed with this new information the team is now examining the attention networks of people with schizophrenia, a disorder characterized in part by poor social function.
The researchers state that persons with schizophrenia have difficulty expressing emotions, responding to social cues and often become socially isolated. They go on to add that right now they’re testing whether these individuals have an impairment to how the VAN is organized or communicates with the rest of the brain. The team go on to concluded that if they do they could potentially tailor a treatment strategy to mitigate that impairment, and maybe even restore some level of social communication that the patient lacked.