It doesn’t take a PhD in neuroscience to know that our capacity to keep multiple things within conscious awareness at the same time is greatly limited, as evidenced by memory-intensive everyday tasks.
According to a group of researchers from the City, University of London, this may be due to miscommunication between regions of the brain responsible for encoding information in real-time.
More specifically, as laid out in a paper out in the journal Cerebral Cortex, the “coupling” — or synchronicity — of brain waves originating from the prefrontal cortex (PFC), the frontal eye fields (FEF), and the lateral intraparietal area (LIP) break down when visual working memory load outstrips capacity.
When this happens, the regions are no longer able to communicate with each other to sustain the proper functioning of working memory.
“At peak memory capacity, the brain signals that maintain memories and guide actions based on these memories, reach their maximum. Above this peak, the same signals break down,” said lead author on the study Dimitris Pinotsis.
While the exact meaning of “peak memory capacity” depends on the specific individual, the average number of objects a person can actively hold in his or her mind without significant impairment tend to be around seven.
Given that working memory correlates robustly with general intelligence, figuring out the limiting factors could help explain how certain psychiatric conditions inhibit cognition in those suffering from them.
The results were achieved by subjecting a group of monkeys to a change-detection task which required them to spot differences between two nearly identical sets of squares on a computer screen.
The crucial finding was that in cases where capacity was nearly or actually exceeded, the coupling of the prefrontal cortex to the FEF and LIP at low frequency all but stopped.
As the PCF has already been shown to employ low-frequency waves to keep working memory in sync, its breakdown might be the decisive factor which limits the whole enterprise.
“We knew that stimulus load degrades stimulus processing in various brain areas, but we hadn’t seen any distinct change that correlated with reaching capacity, but we did see this with feedback coupling. It drops off when the subjects exceeded their capacity. The PFC stops providing feedback coupling to the FEF and LIP,” said lead author on the study Professor Earl Miller.