The human brain's neocortex is responsible for our ability to think, determine, remember recent experiences, and so on.

Neuroscientists have now discovered important portions of the mechanisms underlying these functions. Their discoveries may eventually aid in treating some neuropsychiatric illnesses and brain damage.

Scientists have long known that the neocortex integrates information streams known as feedforward and feedback. The brain's sensory systems transfer data from the periphery (our senses) to the higher-order parts of the neocortex. These high-level brain regions then transmit feedback data to modify and adapt sensory processing.

This two-way communication enables the brain to pay attention, retain short-term memories, and make judgments. "A simple example is when you want to cross a busy road," said corresponding author Gyorgy Lur, PhD, an assistant professor of neurobiology & behaviour in the School of biological sciences.

"There are trees, people, moving vehicles, traffic signals, signs and more. Your higher-level neocortex tells your sensory system which merits attention for deciding when to go across."

The interaction between higher- and lower-level systems also allows us to remember what we saw when we glanced both ways to gather the information. "If you didn't have that short-term memory, you would keep looking back and forth and never move," he said. "In fact, if our feedforward and feedback streams weren't constantly working together, we would do very little except respond by reflexes."

Scientists have not known how neurons in the brain participate in these complicated processes until now. Lur and his colleagues revealed that feedforward and feedback signals converge on single neurons in the neocortex's parietal regions.

The researchers also discovered that different types of cortical neurons integrate the two information streams on significantly different time scales. They identified the cellular and circuit architecture that underpins these distinctions.

"Scientists already knew that integrating multiple senses enhances neuronal responses," Lur said. "If you only see something or just hear it, your reaction time is slower than when experiencing them with both senses simultaneously. We've identified the underlying mechanisms making this possible."

According to the study findings, the same rules hold if one input stream is sensory and the other is cognitive. Understanding these mechanisms is essential for creating future treatments for neuropsychiatric illnesses such as sensory-processing problems, schizophrenia, and ADHD, as well as strokes and other neocortical traumas.

Lur is a member of UC Irvine's centre for the neurobiology of learning and memory, Center for neural circuit mapping, and Centre for hearing research.