Carlo Sestieri, Gordon L. Shulman & Maurizio Corbetta, Washington University School of Medicine
In: The Neuroscience of Attention – ed. George R. Mangun Oxford University Press (2012)
Summary and review of the above chapter
The brain coordinates ongoing goals and expectations with new sensory inputs. Internal neural signals are seen to modulate the perceptions that result from sensory inputs. Top-down signals from the prefrontal cortex bias the sensory system towards stimuli that are relevant for behaviour.
The research of the last 20 years demonstrates a clear divide between sensory input and the internally driven modulation of sensory processing. The dorsal frontoparietal attention network (DAN) is involved in the selection of task-relevant stimuli. The system biases the processing of incoming information towards relevant stimuli. This relates to features such as location, shape, colour and direction of motion. Some areas of DAN relate to object-based attention that does not involve changes of location. Sensory areas specialised for the analysis of different features send inputs to the DAN, which feeds back signals to bias or modulate the activities of these sensory areas. Regions in the DAN respond to behaviourally relevant stimuli in preference to equally strong signals that are not behaviourally relevant.
The frontoparietal has been found to have separate regions for either shifting or maintaining attention. Regions of the dorsal frontparietal that are active during shifting or maintaining attention remain strongly correlated with one another, even when they are at rest, and the DAN is at the same time separate from the sensory, the motor and the default mode networks.
A distinction is made between this type of internally driven voluntary attention on the one hand, and on the other, involuntary attention given to unanticipated inputs from the environment that require a reorienting of attention. The dorsal frontoparietal plus the superior collicus and possibly the pulvinar region of the thalamus are involved in both types of attention. When orienting to an unanticipated stimulus, both the DAN and another system, the ventral frontoparietal attention network (VAN) are involved. The VAN is tuned to all those sensory inputs that do not match expectations.
While the dorsal attentional network focuses on narrow targets, the ventral attentional network works on a broader range of brain regions. The ventral network is specialised in reorienting to a novel stimulus from the environment. The VAN is activated by violations of expectations prompting a need to update the model of the environment. This network has been demonstrated to be independent from the dorsal (DAN) system. The ventral network is also suggested to respond to transitions where one event or sequence of behaviour stops and another starts. It is suggested that the ventral network could provide a reset signal in this t ype of transition, helping with the reorganisation of behaviour. The VAN system like the DAN is thought to work on the basis of a signal’s relevance to behaviour or tasks, as it does not respond to distracter signals of equal strength to attended signals. The basic notion is that there are two attention networks, one for orienting and one for reorienting. The reorienting stage appears to rely on the dorsal network working with the ventral reorienting network.
The source of this task relevance is suggested to be the dorsal network. Importantly, the dorsal frontoparietal network is not seen as the real origin of endogneous or voluntary biases, but rather an intermediate stage that receives bias signals from the brain’s reward system.
Synchronised brain activity looks to be involved in these processes. The frontoparietal control region may be synchronised with activity in the sensory neurons. Thus the frontoparietal control regions can be seen to be synchronised with attended locations, but not synchronised with unattended locations. This can include large scale synchronisation between the frontoparietal control system and the visual cortex. Increases in gamma synchrony are related to decreases in alpha and Beta synchrony. An experiment involving impairment of the frontal eye field (FEF) prevented the drop in the alpha/Beta synchronisation, and in turn impaired the perception of target inputs. This is suggested to indicate that the frontoparietal regions influence the synchronisation of the visual cortex, and facilitates feed forward from the attended sensory locations. A number of studies support the view that synchrony is involved in selective attention and working memory maintenance.