The brain is not one homogeneous mass of neural cells, but it is made up of distinct areas that have specialised functions. This is clearly evident in the part of the brain used for seeing, also called the visual cortex. For example, when we perceive a car on the street, separate brain areas process its texture, colour and motion; these brain areas then interact to tell us a shiny white police car is coming our way (see Figure 1). Many brain areas possess a further internal structure. In visual cortex, a prominent organisational principle of almost every visual area is that of retinotopy; when we perceive the police car from the corner of our eyes (the periphery), different parts of the visual cortex are active than when we directly stare at the police car (the fovea). In other words, there is a one-to-one relationship between where in our environment we perceive an object (like the police car), and which parts of our visual areas become active.
Figure 1. Information from the fovea and periphery is being transmitted via our eyes to the visual cortex in the back of the brain (left). There, it is processed by different brain regions (foveal regions in yellow and peripheral regions in green), which are present on both sides of the brain. Brain activity in fovea-processing regions is highly correlated, as is brain activity in periphery-processing regions, even when the brain is inactive (right). Correlations between fovea-processing and periphery-processing regions are much lower, despite those regions being neighbours. Therefore, activity in the resting brain follows the same organisational principles as the brain’s anatomy suggests.
In humans, the most common method for measuring brain activity is called functional magnetic resonance imaging (fMRI). This technique determines the blood supply to the entire brain; the assumption is that when a certain brain area becomes active, it needs more oxygen and glucose and therefore an increased blood supply. In the past two decades, fMRI has been used increasingly to measure the brain ‘at rest’, for example during sleep. These studies have found that the resting brain still produces a lot of activity, and that this activity is not random, but displays a complex spatial structure. It is unclear from where these patterns emerge. Could it be that they are somehow linked to the underlying anatomical structure of brain areas, such as the retinotopy of the visual cortex?
We investigated this potential link between the structure found in resting brain activity and the brain’s anatomy, by means of fMRI in the visual cortex of 44 participants. Indeed, we found that the activity of the brain at rest mapped onto visual cortex organisation. For example, the activity in the brain regions corresponding to the fovea and periphery display high correlations among themselves; much higher than the correlations between these regions (see Figure 1). In other words, parts of the brain that are activated by the periphery preferentially ‘talk to each other’; they talk much less to those parts of the brain activated by the fovea.
We conclude that the complex structure that is commonly found in the activity of the brain at rest, is tightly linked to the underlying anatomical principles of the brain. This finding could help to make sense of the activity that is measured in diseased brains at rest, such as in schizophrenia and Alzheimer’s disease.
Reference
Functional connectivity patterns of visual cortex reflect its anatomical organization. Genc E*, Schölvinck ML*, Bergmann J, Singer W, Kohler A (2016) *shared first authorship. Cerebral Cortex 26: 3719-3731.