Tag Archives: pulvinar

The pulvinar and attention

The streetlight effect is a type of observational bias where people only look for whatever they are searching for by looking where it is easiest. The parable is told several ways but includes the following details: A policeman sees a drunk man searching for something under a streetlight and asks what the drunk has lost. He says he lost his keys and they both look under the streetlight together. After a few minutes the policeman asks if he is sure he lost them here, and the drunk replies, no, that he lost them in the park. The policeman asks why he is searching here, and the drunk replies, “this is where the light is.” This is how Wikipedia tells how this old joke gave the streetlight effect its name. The effect seems to me to be common in neuroscience. Many researchers seem to ignore the thalamus and concentrate only on the cortex when trying to understand perception, consciousness, attention, and working memory. Just because it is easier to look only at activity in the cortex does not mean that everything happens there.

 

Part of the thalamus, the pulvinar, has been shown to be involved in attention, especially visual attention. A recent paper (see citation) examines the pulvinar’s role in maintaining attention. This is another bit of evidence pointing to the importance of thalamus-cortex interaction in the areas of perception, consciousness and attention.

 

Attention is marked by synchronous firing in a number of cortical areas that represent the visual item being held in attention. “Simultaneous neural recordings from two cortical areas have suggested that this selective routing depends on the degree of synchrony between neuronal groups in each cortical area . However, it is unclear how different cortical areas synchronize their activity. Although direct interaction between two cortical areas may give rise to their synchrony, an alternative possibility is that a third area, connected to both of them, mediates cortical synchronization…We therefore hypothesized that the pulvinar increases synchrony between sequential processing stages across the visual cortex during selective attention. ”

 

The experimental setup was a screen on which appeared a short cue as to where a trigger was going to appear. The monkey had to hold this cued location in mind during a delay before the trigger appeared. The monkey was to react to the type of trigger and not be distracted by other similar images in other locations. The activity in various brain regions could be examined before, during and after the attention that was forced by the delay between cue and trigger. The activity in three areas was followed: two regions along the ventral visual pathway that are synchronous during visual attention and an area of the pulvinar that was in two-way interaction with both these visual areas. The ventral stream is the ‘what’ visual stream that is involved in object recognition, episodic memory and consciousness (as opposed to the ‘where’ dorsal stream involved in motor control and is largely unconscious). During the attention period these areas had increased activity and were synchronized in the alpha and gamma bands. Further, using conditional Granger causality calculations, it was the pulvinar that was influencing the two visual cortex areas rather than the other way around and rather than the two visual areas influencing each other. This pulvinar driving was only seen during the attention period.

 

The hypothesis, that the pulvinar nucleus of the thalamus maintains attention by increasing “the synchrony between sequential processing stages across the visual cortex”, has some strong corroborating evidence now. Here is the paper’s abstract:

 

Selective attention mechanisms route behaviorally relevant information through large-scale cortical networks. Although evidence suggests that populations of cortical neurons synchronize their activity to preferentially transmit information about attentional priorities, it is unclear how cortical synchrony across a network is accomplished. Based on its anatomical connectivity with the cortex, we hypothesized that the pulvinar, a thalamic nucleus, regulates cortical synchrony. We mapped pulvino-cortical networks within the visual system, using diffusion tensor imaging, and simultaneously recorded spikes and field potentials from these interconnected network sites in monkeys performing a visuospatial attention task. The pulvinar synchronized activity between interconnected cortical areas according to attentional allocation, suggesting a critical role for the thalamus not only in attentional selection but more generally in regulating information transmission across the visual cortex.

 

ResearchBlogging.org

Saalmann, Y., Pinsk, M., Wang, L., Li, X., & Kastner, S. (2012). The Pulvinar Regulates Information Transmission Between Cortical Areas Based on Attention Demands Science, 337 (6095), 753-756 DOI: 10.1126/science.1223082

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