Focusing on attention
29 Jun, 2007 03:15 pm
There are many things in the world around us, too many for the brain to process in detail at the same time. A lot of these things, however, are not always important to us. Ideally, we would spend more time and resources processing the important things and less time on the rest. Attention helps us to do just that, by selecting what is potentially important to us, so that it can be processed in detail by the brain.
aDepartment of Psychology, Royal Holloway, University of London
bInstitute for Information Transmission Problems, Russian Academy of Sciences
cDepartment of Optometry and Vision Sciences, University of Melbourne
Sometimes this can go wrong. For instance, a syndrome referred to as spatial neglect can occur after strokes. Patients with spatial neglect will not notice things in the space around one side of their bodies, usually their left side. Many patients are not even aware that they have this problem.
Let us now look more closely at how the brain allows us to pay attention to the things we see. Information from the world around us is sent by the eyes to the back of the brain, also known as the visual cortex. Different parts of the visual cortex process information from different locations around us. When we pay attention to a particular location, then there is a selective increase in the electrical activity of the brain cells that process information from this location.
The question is: what causes this increase in electrical activity in the visual cortex? A higher area of the brain called the posterior parietal cortex is involved in determining the importance of locations around us (in fact, the posterior parietal cortex is part of a network of brain areas involved in attention). To test how this area affects other parts of the brain, we simultaneously measured the electrical activity of brain cells in the posterior parietal cortex and visual cortex of macaque monkeys, while they played video games. Our research1,2 shows that electrical signals are sent from the posterior parietal cortex to the visual cortex, providing “feedback” as to which locations around us are important. It is these signals that increase the electrical activity in visual cortex, and it is this interaction between the brain areas that is critical for attention.
Our data suggest that the feedback can increase the electrical activity in visual cortex in three ways. First, more electrical signals can be sent from the posterior parietal cortex to the visual cortex. Incoming electrical signals increase the electrical activity in the visual cortex – the more incoming signals, the more activity in the visual cortex.
Second, many brain cells in the posterior parietal cortex send electrical signals to the visual cortex. If the signals from a number of different brain cells in the posterior parietal cortex are synchronized, then their impact on the visual cortex is increased. This is similar to a situation where your car breaks down and you have a number of friends to help push. The car moves more easily when you all push at the same time, rather than if you push one at a time. When incoming electrical signals act on the visual cortex at the same time, they more easily increase the electrical activity in the visual cortex.
Third and finally, the electrical activity of brain cells can go up and down in a repeating rhythm, that is, the activity can oscillate. If the electrical activity of brain cells in the visual cortex is up, then electrical signals arriving from the posterior parietal cortex have a greater effect (in comparison with the scenario where signals arrive when the activity in the visual cortex is down). This can be made more likely by synchronizing oscillations in the posterior parietal cortex and visual cortex.
The three mechanisms outlined above may well play a more general role in cognition than just attention. These mechanisms may be fundamental ways to increase the impact of electrical signals, that is, information, sent between any two brain areas. Different pieces of information will be important under different circumstances. So the ability to weight information according to circumstance allows us to flexibly interact with our environment.
1 Saalmann YB, Pigarev IN, Vidyasagar TR (2007) Neural mechanisms of visual attention: how top-down feedback highlights relevant locations. Science 316: 1612-1615.
2 Experiments were carried out at the University of Melbourne, Australia, and were supported by grants from the National Health and Medical Research Council of Australia.