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The functional role of the inferior parietal lobe in the dorsal and ventral stream dichotomy.

Singh-Curry V, Husain M - Neuropsychologia (2008)

Bottom Line: Some recent proposals have attempted to integrate aspects of IPL function that were not hitherto dealt with well, such as differences between the left and right hemisphere and the role of the right IPL in responding to salient environmental events.Here we critically appraise existing proposals regarding the functional architecture of the visual system, with special emphasis on the role of this region, particularly in the right hemisphere.We review evidence that shows the right IPL plays an important role in two different, but broadly complementary, aspects of attention: maintaining attentive control on current task goals as well as responding to salient new information or alerting stimuli in the environment.

View Article: PubMed Central - PubMed

Affiliation: UCL Institute of Cognitive Neuroscience, London, United Kingdom.

ABSTRACT
Current models of the visual pathways have difficulty incorporating the human inferior parietal lobe (IPL) into dorsal or ventral streams. Some recent proposals have attempted to integrate aspects of IPL function that were not hitherto dealt with well, such as differences between the left and right hemisphere and the role of the right IPL in responding to salient environmental events. However, we argue that these models also fail to capture adequately some important findings regarding the functions of the IPL. Here we critically appraise existing proposals regarding the functional architecture of the visual system, with special emphasis on the role of this region, particularly in the right hemisphere. We review evidence that shows the right IPL plays an important role in two different, but broadly complementary, aspects of attention: maintaining attentive control on current task goals as well as responding to salient new information or alerting stimuli in the environment. In our view, findings from functional imaging, electrophysiological and lesion studies are all consistent with the view that this region is part of a system that allows flexible reconfiguration of behaviour between these two alternative modes of operation. Damage to the right IPL leads to deficits in both maintaining attention and also responding to salient events, impairments that contribute to hemineglect, the classical syndrome that follows lesions of this region.

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Postulated relationship between locus coeruleus activity, posterior parietal function and behavioural state. (A) The relationship between tonic levels of noradrenergic activity in the locus coeruleus (LC) and the ability to sustain attention on a task follows an inverted U-shaped function. Low levels of tonic activity are associated with drowsiness, moderate levels with efficient task-engaged behaviour and higher levels with a more distractible, exploratory state. (B) In the task-engaged state, LC tonic activity is moderate, with optimal phasic bursts in response to task-related targets (f, firing rate of LC neurons; t, time or latency). This leads to a P3b potential in the posterior parietal cortex, facilitating accurate task performance. Novel or infrequently occurring events (of no task-relevance) can also produce phasic LC responses. These are associated with a P3a potential in parietal cortex, which is generally smaller than the P3b potential. The P3a does not correlate with behavioural responses when performance is task-engaged. Note that, in contrast to either target or infrequent novel stimuli, frequently occurring task-irrelevant stimuli do not evoke P3 responses.
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fig7: Postulated relationship between locus coeruleus activity, posterior parietal function and behavioural state. (A) The relationship between tonic levels of noradrenergic activity in the locus coeruleus (LC) and the ability to sustain attention on a task follows an inverted U-shaped function. Low levels of tonic activity are associated with drowsiness, moderate levels with efficient task-engaged behaviour and higher levels with a more distractible, exploratory state. (B) In the task-engaged state, LC tonic activity is moderate, with optimal phasic bursts in response to task-related targets (f, firing rate of LC neurons; t, time or latency). This leads to a P3b potential in the posterior parietal cortex, facilitating accurate task performance. Novel or infrequently occurring events (of no task-relevance) can also produce phasic LC responses. These are associated with a P3a potential in parietal cortex, which is generally smaller than the P3b potential. The P3a does not correlate with behavioural responses when performance is task-engaged. Note that, in contrast to either target or infrequent novel stimuli, frequently occurring task-irrelevant stimuli do not evoke P3 responses.

Mentions: The relationship between tonic noradrenergic activity and function is thought to follow an inverted U-shaped curve (Fig. 7A), with an optimal level of focussed performance being associated with a moderate level of noradrenaline, while low noradrenergic levels are associated with drowsiness and high levels with distractibility (Aston-Jones & Cohen, 2005). Importantly, the level of tonic activity appears to influence the extent of phasic noradrenaline release. At low tonic levels, when the animal is drowsy, there is very little phasic activity, and similarly at very high tonic levels. But between these two extremes – at moderate tonic noradrenergic levels – phasic LC bursts are most effective and are strongly correlated with accurate target detection (Aston-Jones, Rajkowski, Kubiak, & Alexinsky, 1994) and, by inference, the P3b potential recorded over parietal cortex in response to salient task-related stimuli (Fig. 7B). It is in this condition that behaviour seems to be most easily maintained on task demands, corresponding to our view of the state of sustained attention in human observers.


The functional role of the inferior parietal lobe in the dorsal and ventral stream dichotomy.

Singh-Curry V, Husain M - Neuropsychologia (2008)

Postulated relationship between locus coeruleus activity, posterior parietal function and behavioural state. (A) The relationship between tonic levels of noradrenergic activity in the locus coeruleus (LC) and the ability to sustain attention on a task follows an inverted U-shaped function. Low levels of tonic activity are associated with drowsiness, moderate levels with efficient task-engaged behaviour and higher levels with a more distractible, exploratory state. (B) In the task-engaged state, LC tonic activity is moderate, with optimal phasic bursts in response to task-related targets (f, firing rate of LC neurons; t, time or latency). This leads to a P3b potential in the posterior parietal cortex, facilitating accurate task performance. Novel or infrequently occurring events (of no task-relevance) can also produce phasic LC responses. These are associated with a P3a potential in parietal cortex, which is generally smaller than the P3b potential. The P3a does not correlate with behavioural responses when performance is task-engaged. Note that, in contrast to either target or infrequent novel stimuli, frequently occurring task-irrelevant stimuli do not evoke P3 responses.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2697316&req=5

fig7: Postulated relationship between locus coeruleus activity, posterior parietal function and behavioural state. (A) The relationship between tonic levels of noradrenergic activity in the locus coeruleus (LC) and the ability to sustain attention on a task follows an inverted U-shaped function. Low levels of tonic activity are associated with drowsiness, moderate levels with efficient task-engaged behaviour and higher levels with a more distractible, exploratory state. (B) In the task-engaged state, LC tonic activity is moderate, with optimal phasic bursts in response to task-related targets (f, firing rate of LC neurons; t, time or latency). This leads to a P3b potential in the posterior parietal cortex, facilitating accurate task performance. Novel or infrequently occurring events (of no task-relevance) can also produce phasic LC responses. These are associated with a P3a potential in parietal cortex, which is generally smaller than the P3b potential. The P3a does not correlate with behavioural responses when performance is task-engaged. Note that, in contrast to either target or infrequent novel stimuli, frequently occurring task-irrelevant stimuli do not evoke P3 responses.
Mentions: The relationship between tonic noradrenergic activity and function is thought to follow an inverted U-shaped curve (Fig. 7A), with an optimal level of focussed performance being associated with a moderate level of noradrenaline, while low noradrenergic levels are associated with drowsiness and high levels with distractibility (Aston-Jones & Cohen, 2005). Importantly, the level of tonic activity appears to influence the extent of phasic noradrenaline release. At low tonic levels, when the animal is drowsy, there is very little phasic activity, and similarly at very high tonic levels. But between these two extremes – at moderate tonic noradrenergic levels – phasic LC bursts are most effective and are strongly correlated with accurate target detection (Aston-Jones, Rajkowski, Kubiak, & Alexinsky, 1994) and, by inference, the P3b potential recorded over parietal cortex in response to salient task-related stimuli (Fig. 7B). It is in this condition that behaviour seems to be most easily maintained on task demands, corresponding to our view of the state of sustained attention in human observers.

Bottom Line: Some recent proposals have attempted to integrate aspects of IPL function that were not hitherto dealt with well, such as differences between the left and right hemisphere and the role of the right IPL in responding to salient environmental events.Here we critically appraise existing proposals regarding the functional architecture of the visual system, with special emphasis on the role of this region, particularly in the right hemisphere.We review evidence that shows the right IPL plays an important role in two different, but broadly complementary, aspects of attention: maintaining attentive control on current task goals as well as responding to salient new information or alerting stimuli in the environment.

View Article: PubMed Central - PubMed

Affiliation: UCL Institute of Cognitive Neuroscience, London, United Kingdom.

ABSTRACT
Current models of the visual pathways have difficulty incorporating the human inferior parietal lobe (IPL) into dorsal or ventral streams. Some recent proposals have attempted to integrate aspects of IPL function that were not hitherto dealt with well, such as differences between the left and right hemisphere and the role of the right IPL in responding to salient environmental events. However, we argue that these models also fail to capture adequately some important findings regarding the functions of the IPL. Here we critically appraise existing proposals regarding the functional architecture of the visual system, with special emphasis on the role of this region, particularly in the right hemisphere. We review evidence that shows the right IPL plays an important role in two different, but broadly complementary, aspects of attention: maintaining attentive control on current task goals as well as responding to salient new information or alerting stimuli in the environment. In our view, findings from functional imaging, electrophysiological and lesion studies are all consistent with the view that this region is part of a system that allows flexible reconfiguration of behaviour between these two alternative modes of operation. Damage to the right IPL leads to deficits in both maintaining attention and also responding to salient events, impairments that contribute to hemineglect, the classical syndrome that follows lesions of this region.

Show MeSH
Related in: MedlinePlus