Functional evolution of new and expanded attention networks in humans :: Gaurav Patel, Danica Yang et al :: PNAS
Summary and review of the above paper
Macaque monkeys are often used as models in neuroscience. However, there are important differences between macaques and humans. Humans have a larger dorsal attention network, indicating that evolution has augmented this network. Biases in visual searches are different as between the two species, and aspects of the ventral attention system found in humans are not present in macaques.
Attention is seen to function in two ways, firstly stimulus driven, bottom-up attention, and secondly goal-directed top-down attention. Recent research indicates two attention networks, the dorsal-attention network comprising the frontal eye-fields (FEF) plus the intraparietal sulcus (IPS), and the ventral attention network centred around the temporoparietal junction (TPJ).
The temporoparietal junction
In contrast to the more widespread attention of the dorsal network, the TPJ only reacts to behaviourally relevant stimuli, and particularly stimuli that are unexpected or cause reorientation of attention. Damage to the TPJ reduces the ability to respond to such novel stimuli. There is interaction between the dorsal and ventral attention networks, and between both of these and the visual system. During top-down, goal-directed activity, the dorsal-attention network is enhanced for selected stimuli while the TPJ is deactivated so as not to create distraction.
Although there are some differences between macaques and humans in the functioning of the dorsal-attention system, the most striking difference is the role of the TPJ in attention, something that appears to be lacking in macaques. Deactivation of the TPJ in humans is related to attention or working-memory load.
In humans, more cortical space is devoted to the inferior parietal lobule at the junction of the temporal and parietal lobes. It is suggested that with humans the ventral attention system may be used to deal with social cues rather than physical objects. Areas in or near the TPJ deal with the processing of faces, intentions of others and gaze direction, abilities that are enhanced in humans relative to other species.
The paper emphasises the need to recognise important differences between humans and macaques when undertaking neuroscience studies.
Dorsal and ventral attention systems :: Simone Vossel, Joy Geng, Gereon Fink :: Neuroscientist, April 20 2014, pp. 150-9
Summary and review of the above paper
Researchers, Corbetta and Shulman introduced the concept of distinct attention systems in the human brain at the beginning of this century. The top-down dorsal-frontoparietal system involving intraprietal sulcus and the frontal eye fields (FEF) generating the voluntary direction of attention to particular locations or objects while the ventral-frontoparietal system deal with unexpected features.
The ventral attention network involves the ventral-frontal cortex and the temporoparietal junction (TPJ), and usually responds to behaviourally relevant but unexpected stimuli. It is recognised that the biasing of sensory areas towards particular stimuli derives from the frontoparietal cortex. Imaging studies have shown the causal connection between frontoparietal and sensory regions involve the intraparietal sulcus and the FEF. These two areas have been shown to have top-down influences on the orienting of attention. These top-down effects are known to out-weigh bottom up effects from the visual cortex.
The ventral attention system is more immediately stimulus driven. Activity in the key area of the TPJ is deactivated during top-down directed visual search of visual working memory load. The TPJ is seen as being involved with theory of mind and other social cognition. This system might be triggered not just by external stimuli but also by memories. There is interplay between the two systems and this seems to be controlled by frontal areas such as the inferior and middle frontal gyrus.
Objective analysis of neural cause-and-effect
These conclusions are based on methods for analysing causality within the brain. It is relevant for consciousness studies that cause-and-effect processes in the brain are no longer the realm of the arbitrary dictates of philosophers, but are now the subject of objective analysis. Dynamic causal modelling (DCM) and Grainger causality are two methods used. Grainger causality has been used to demonstrate the neural connectivity of top-down frontal influences on the visual system, and DCM has also been used to map connectivity with the visual system.