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The Attentional Network Model

Attention
Attention

One of the most popular definitions of attention comes from William James who stated that attention is taking possession of the mind to focus on one thing out of several possible options. It is defined as having several essential components such as focalisation, concentration and the ability to withdraw from one thing to effectively deal with others

3 Separate Components
Michael Posners theory of attention proposes that attention is not seen as a unitary concept but rather three attentional networks. These are defined as alerting, orienting and executive function. These three networks interact in many ways, however the operations of these networks have a degree of functional and anatomical independence (Razz, 2004).

Alerting
The alerting component of the attentional network model is achieving and maintaining an alert state. Alerting is thought to involve the locus coeruleus with imaging studies reporting an activation in this region following warning signals. Other regions of the brain thought to be active during the alerting aspect of attention are frontal and parietal regions of the cortex as well as reports of the thalamic region having involvement. The involvement of the locus coeruleus supports reports of the involvement of the neurotransmitter Norepinephrine along with other evidence as Norepinephrine includes major nodes in the frontal and parietal regions of the cortex. Both human and animal studies have linked norepinephrine with alerting and warning signal effects. Drug studies show that alerting decreases when Norepinephrine inhibitors are present and increases when drugs that increase Norepinephrine release are present. The right hemisphere is reported to be involved in slower alerting such as tonic alerting, whereas the rapid phasing alerting is seen to involve the left hemisphere. This has been reported during attention tasks that measure the alerting network of attention. There are numerous attention based tasks that allow attention to be measured. Some of the tasks previously used in studies to measure tonic alerting are vigilance task tests. These tasks are used to measure a persons sustained vigilance and has shown reliance of the right cerebral cortex. Cueing task tests have been used to measure phasic alerting. In this task using a warning signal prior to a target event produces a phasic change in alertness.

Orienting
The orienting attentional network functions to select and prioritise information from a sensory input. Orienting involves posterior brain areas including the temporal parietal junction which is involved with breaking the focus of attention. Other regions involved during orienting are the superior parietal lobe, frontal eye fields and the superior colliculus. Studies have shown the neurotransmitter Norepinephrine doesn’t seem to have an influence on orienting, however acetycholine and the cholinergic systems in the basal forebrain has been seen to affect orienting but not alerting. Drug studies carried out demonstrated this with an increase in acetycholinergic release causing an increase in orienting attention and the ability to shift attention and an attenuation in acetycholoinergic release resulting in a decrease of orienting. Tasks used to measure the orienting component of the attentional networks are variations of a cueing task, the most popular being the posner cueing task. This involves presentations of arrow cues followed by a visual stimulus appearing either in the expected location based on the arrow or in the opposite location. The miscued stimulus means participants have to break their focus and switch location which is measured via eye movement tracking.

Executive Function
The executive attention network involves error detection, conflict resolvement, managing cognitive load and functions to block potentially distracting information from the focus of the prioritised information. Executive function has been reported to involve the anterior cingulate which is associated with maintaining ongoing task performance. Other regions associated with the executive function component of the attenional networks are the lateral prefrontal cortex and the basal ganglia. Studies have shown the importance of the neurotransmitter Dopamine on performance of tasks that involve the executive function and the lateral prefrontal cortex. Imaging studies also show dopamine receptors to be expressed within the cingulate cortex Tasks used to measure the executive function component of the attentional networks typically involve Stroop tasks, spatial conflict tasks and the flanker task which all require focused attention to resolve conflict

Other attention theories that support
Other theories that offer explanations for the mechanisms behind attention have also supported the idea of there being a network of components as apposed to one unitary system and that there is a process of priorotising information when it is being processed. Posner proposed the spotlight attention theory to go alongside his attentional networks theory. This theory demonstrates a metaphoric spotlight beam that can only shine light on one thing, in the same way that attention cannot attend to everything at once and thus has to select something to focus on. The filter model devised by Broadbent (1958) also supports the attentional networks theory. Within this model it is demonstrated that after initial processing of the stimuli there is a system that gives priority to minor parts of the information, then a filter excludes irrelevant information thus enabling the system to deal efficiently with task-relevant targets. A similar theory to the filter model is the Triesman attenuation theory. It is proposed that when information is processed, instead of eliminating information through a filter, all the unattended information is attenuated.

Attention deficits that support the model
As well as other attention theories, another aspect to consider as evidence for Posners attentional networks theory is to look at attentional deficits. Attention deficit hyperactivity disorder is one disorder where imaging studies have supported the anatomy of the attention networks theory. In a study using large deformation diffeomorphic metric mapping (LDDMM) to examine ADHD it was demonstrated that ADHD affected participants had significantly smaller basal ganglia volume and shape. Magnetic Resonance Imaging (MRI) studies also coincide with these results showing differences in the volume of globus pallidus in children diagnosed ADHD. Intervention studies over the years have reported that the use of computer based tasks combining vigilance and executive attention requirements have shown improvement in a number of attention measures in children with ADHD.