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Distinct Neural Substrates for Maintaining Locations and Spatial Relations in Working Memory

View Article: PubMed Central - PubMed

ABSTRACT

Previous work has demonstrated a distinction between maintenance of two types of spatial information in working memory (WM): spatial locations and spatial relations. While a body of work has investigated the neural mechanisms of sensory-based information like spatial locations, little is known about how spatial relations are maintained in WM. In two experiments, we used fMRI to investigate the involvement of early visual cortex in the maintenance of spatial relations in WM. In both experiments, we found less quadrant-specific BOLD activity in visual cortex when a single spatial relation, compared to a single spatial location, was held in WM. Also across both experiments, we found a consistent set of brain regions that were differentially activated during maintenance of locations vs. relations. Maintaining a location, compared to a relation, was associated with greater activity in typical spatial WM regions like posterior parietal cortex and prefrontal regions. Whereas maintaining a relation, compared to a location, was associated with greater activity in the parahippocampal gyrus and precuneus/retrosplenial cortex. Further, in Experiment 2 we manipulated WM load and included trials where participants had to maintain three spatial locations or relations. Under this high load condition, the regions sensitive to locations vs. relations were somewhat different than under low load. We also identified regions that were sensitive to load specifically for location or relation maintenance, as well as overlapping regions sensitive to load more generally. These results suggest that the neural substrates underlying WM maintenance of spatial locations and relations are distinct from one another and that the neural representations of these distinct types of spatial information change with load.

No MeSH data available.


Experiment 2 trial schematics showing example Location and Relation trials. For low load Location trials participants were instructed to imagine a line between two sample circles (shown here only for illustration purposes), hold the location of that line in memory across a delay and then decide if a test circle fell in that location or not. For high load Location trials participants maintained the locations of three circles in memory and then decided if a test circle fell in one of those locations or in a completely new location. For low load Relation trials participants maintained the vertical relationship (above/below) of two sample circles and then decided if two test circles were in the same relationship. For high load Relation trials participants maintained the three vertical relationships between three sample circles and then decided if the circles of one of those pairs were presented in the same relationship at test.
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Figure 2: Experiment 2 trial schematics showing example Location and Relation trials. For low load Location trials participants were instructed to imagine a line between two sample circles (shown here only for illustration purposes), hold the location of that line in memory across a delay and then decide if a test circle fell in that location or not. For high load Location trials participants maintained the locations of three circles in memory and then decided if a test circle fell in one of those locations or in a completely new location. For low load Relation trials participants maintained the vertical relationship (above/below) of two sample circles and then decided if two test circles were in the same relationship. For high load Relation trials participants maintained the three vertical relationships between three sample circles and then decided if the circles of one of those pairs were presented in the same relationship at test.

Mentions: Trial schematics for Experiment 2 are shown in Figure 2. A trial began with a 400 ms fixation cross (0.12°), presented in the middle of the screen. Next, a 500 ms cue indicated whether participants were to remember a particular location (“Location trial,” cued by the word “Item”) or the relative spatial relationship between the items presented (“Relation trial,” cued by the word “Relation”). A sample array was then presented for 500 ms, which contained two or three colored circles (each subtending 0.5° of visual angle). The presentation of the sample circles was restricted to one quadrant of the display. The color of each circle was chosen randomly without replacement from red, green, yellow, and blue. After a 8 s delay period, a test array was displayed for 500 ms. Participants had an additional 1000 ms after the offset of the test array to respond, during which there was only a fixation cross on the screen. Finally, a 100 ms feedback display was presented. After every 13 trials, the word “REST” was presented in the center of the screen for 11 s.


Distinct Neural Substrates for Maintaining Locations and Spatial Relations in Working Memory
Experiment 2 trial schematics showing example Location and Relation trials. For low load Location trials participants were instructed to imagine a line between two sample circles (shown here only for illustration purposes), hold the location of that line in memory across a delay and then decide if a test circle fell in that location or not. For high load Location trials participants maintained the locations of three circles in memory and then decided if a test circle fell in one of those locations or in a completely new location. For low load Relation trials participants maintained the vertical relationship (above/below) of two sample circles and then decided if two test circles were in the same relationship. For high load Relation trials participants maintained the three vertical relationships between three sample circles and then decided if the circles of one of those pairs were presented in the same relationship at test.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121279&req=5

Figure 2: Experiment 2 trial schematics showing example Location and Relation trials. For low load Location trials participants were instructed to imagine a line between two sample circles (shown here only for illustration purposes), hold the location of that line in memory across a delay and then decide if a test circle fell in that location or not. For high load Location trials participants maintained the locations of three circles in memory and then decided if a test circle fell in one of those locations or in a completely new location. For low load Relation trials participants maintained the vertical relationship (above/below) of two sample circles and then decided if two test circles were in the same relationship. For high load Relation trials participants maintained the three vertical relationships between three sample circles and then decided if the circles of one of those pairs were presented in the same relationship at test.
Mentions: Trial schematics for Experiment 2 are shown in Figure 2. A trial began with a 400 ms fixation cross (0.12°), presented in the middle of the screen. Next, a 500 ms cue indicated whether participants were to remember a particular location (“Location trial,” cued by the word “Item”) or the relative spatial relationship between the items presented (“Relation trial,” cued by the word “Relation”). A sample array was then presented for 500 ms, which contained two or three colored circles (each subtending 0.5° of visual angle). The presentation of the sample circles was restricted to one quadrant of the display. The color of each circle was chosen randomly without replacement from red, green, yellow, and blue. After a 8 s delay period, a test array was displayed for 500 ms. Participants had an additional 1000 ms after the offset of the test array to respond, during which there was only a fixation cross on the screen. Finally, a 100 ms feedback display was presented. After every 13 trials, the word “REST” was presented in the center of the screen for 11 s.

View Article: PubMed Central - PubMed

ABSTRACT

Previous work has demonstrated a distinction between maintenance of two types of spatial information in working memory (WM): spatial locations and spatial relations. While a body of work has investigated the neural mechanisms of sensory-based information like spatial locations, little is known about how spatial relations are maintained in WM. In two experiments, we used fMRI to investigate the involvement of early visual cortex in the maintenance of spatial relations in WM. In both experiments, we found less quadrant-specific BOLD activity in visual cortex when a single spatial relation, compared to a single spatial location, was held in WM. Also across both experiments, we found a consistent set of brain regions that were differentially activated during maintenance of locations vs. relations. Maintaining a location, compared to a relation, was associated with greater activity in typical spatial WM regions like posterior parietal cortex and prefrontal regions. Whereas maintaining a relation, compared to a location, was associated with greater activity in the parahippocampal gyrus and precuneus/retrosplenial cortex. Further, in Experiment 2 we manipulated WM load and included trials where participants had to maintain three spatial locations or relations. Under this high load condition, the regions sensitive to locations vs. relations were somewhat different than under low load. We also identified regions that were sensitive to load specifically for location or relation maintenance, as well as overlapping regions sensitive to load more generally. These results suggest that the neural substrates underlying WM maintenance of spatial locations and relations are distinct from one another and that the neural representations of these distinct types of spatial information change with load.

No MeSH data available.