Human brain connections

The Human ConnectomeFor questions about why people often think, act, and perceive the world so differently, the brain is clearly an obvious place to look for answers. However, because the human brain is packed with tens of billions of neurons, which together make trillions of connections, knowing exactly where and how to look remains profoundly challenging.

Undaunted by these complexities, researchers involved in the NIH-funded Human Connectome Project (HCP) have been making progress, as shown by some intriguing recent discoveries. In a study published in Nature Neuroscience [1], an HCP team found that the brains of individuals with “positive” traits—such as strong cognitive skills and a healthy sense of well-being—show stronger connectivity in certain areas of the brain than do those with more “negative” traits—such as tendencies toward anger, rule-breaking, and substance use. While these findings are preliminary, they suggest it may be possible one day to understand, and perhaps even modify, the connections within the brain that are associated with human behavior in all its diversity.

In the new study, Stephen Smith of the Oxford University Centre for Functional MRI of the Brain, United Kingdom and his colleagues measured for an hour the patterns of neural activity and connectivity among 200 distinct brain regions in 461 HCP participants lying still in an MRI scanner. The participants also completed a series of tests and questionnaires to collect demographic and behavioral data, including IQ, memory, language performance, vocabulary, life satisfaction, income, attention, sleep quality, and drug and alcohol use.

Analyzing the correlations among variables in the two datasets, the researchers discovered a clear pattern: people characterized by stronger connections among certain brain regions also scored more highly on measures typically deemed to be socially positive. They also generally made more money, were more highly educated, and scored higher on tests of memory and attention. By comparison, those found to have weaker connections scored less well on memory tests, were more prone to anger, had trouble sleeping, and were more likely to smoke.

The researchers noted the stronger connections that were associated with positive traits seem to overlap with an interconnected brain system neuroscientists refer to as the “default mode network.” This network describes a form of resting brain activity associated with many aspects of higher-level human cognition, including memory, imagination, decision making, and spatial reasoning. This pattern tends to activate, for example, when people focus internally, daydreaming about the future or remembering the past.

It’s important to point out that the new study shows only a correlation between a particular pattern of brain connectivity and certain measures of performance, lifestyle, and ability. It’s also important to note that brain connections are not predetermined or inflexible. Rather, our experiences, both good and bad, seem to modify them in complex and largely undetermined ways. Determining whether particular traits cause a particular pattern of brain connectivity—or vice versa—will be interesting to unravel in the years ahead. It’s easy to imagine that, in many cases, the answer will involve the interplay of both.

In addition to the HCP findings, another fascinating study led by scientists supported by the NIH-funded Brain Research through Advancing Innovating Neurotechnologies (BRAIN) Initiative and reported in Cell [2] reveals a unique set of stem cells are present in the human cerebral cortex. This cellular support system helps to explain how the primate brain could expand over the course of evolutionary time, endowing humans with our characteristically large brains in comparison to other mammals.

As for the HCP, there’s plenty more to come. As the project expands to include 1, 200 healthy adults, including twin pairs and their siblings, scientists can begin to tease out the relative contributions of genes and the environment in shaping the wiring diagram of the brain. More discoveries are anticipated.

References:

[1] A positive-negative mode of population covariation links brain connectivity, demographics and behavior. Smith SM, Nichols TE, Vidaurre D, Winkler AM, Behrens TE, Glasser MF, Ugurbil K, Barch DM, Van Essen DC, Miller KL.Nat Neurosci. 2015 Sep 28. [Epub ahead of print]

[2] Molecular Identity of Human Outer Radial Glia during Cortical Development.Pollen AA, Nowakowski TJ, Chen J, Retallack H, Sandoval-Espinosa C, Nicholas CR, Shuga J, Liu SJ, Oldham MC, Diaz A, Lim DA, Leyrat AA, West JA, Kriegstein AR.Cell. 2015 Sep 24;163(1):55-67.

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