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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 1 trial schematics showing example (A) Location and (B) Relation trials. Participants were always cued to make a covert shift of attention to either the left or right hemifield via an arrow cue. For Location trials, participants were cued “Item” which instructed them to imagine a line between the two sample array circles (shown here only for illustration purposes) and hold the location of that line in memory over the delay. At test, participants indicated whether the two test circles straddled the imaginary line. For Relation trials, participants were cued “Relation” which instructed them to remember the relative vertical relationship of the two circles, using the red-center as the reference. At test, participants indicated whether the test circles had the same relationship or not.
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Figure 1: Experiment 1 trial schematics showing example (A) Location and (B) Relation trials. Participants were always cued to make a covert shift of attention to either the left or right hemifield via an arrow cue. For Location trials, participants were cued “Item” which instructed them to imagine a line between the two sample array circles (shown here only for illustration purposes) and hold the location of that line in memory over the delay. At test, participants indicated whether the two test circles straddled the imaginary line. For Relation trials, participants were cued “Relation” which instructed them to remember the relative vertical relationship of the two circles, using the red-center as the reference. At test, participants indicated whether the test circles had the same relationship or not.

Mentions: As shown in Figure 1, all stimuli were presented on a 50% gray background. A trial began with a 1000 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”). This task cue was followed by a 200 ms arrow cue, which indicated whether the left or right hemifield should be attended. A sample array was then presented for 500 ms, which contained four circles of varying shades of gray (each subtending 0.3° of visual angle), 2 in each hemifield. One circle in each hemifield contained a red center (0.1°). After a 8 s delay period, four more circles, two in each hemifield, were presented as the test array for 1500 ms during which the participant entered a response. The test array was followed by a 200 ms feedback period where the fixation cross turned green for a correct response, red for an incorrect response, and blue if the response was slower than 1500 ms. After every 10 trials, the word “REST” was presented in the center of the screen for 12 s.


Distinct Neural Substrates for Maintaining Locations and Spatial Relations in Working Memory
Experiment 1 trial schematics showing example (A) Location and (B) Relation trials. Participants were always cued to make a covert shift of attention to either the left or right hemifield via an arrow cue. For Location trials, participants were cued “Item” which instructed them to imagine a line between the two sample array circles (shown here only for illustration purposes) and hold the location of that line in memory over the delay. At test, participants indicated whether the two test circles straddled the imaginary line. For Relation trials, participants were cued “Relation” which instructed them to remember the relative vertical relationship of the two circles, using the red-center as the reference. At test, participants indicated whether the test circles had the same relationship or not.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: Experiment 1 trial schematics showing example (A) Location and (B) Relation trials. Participants were always cued to make a covert shift of attention to either the left or right hemifield via an arrow cue. For Location trials, participants were cued “Item” which instructed them to imagine a line between the two sample array circles (shown here only for illustration purposes) and hold the location of that line in memory over the delay. At test, participants indicated whether the two test circles straddled the imaginary line. For Relation trials, participants were cued “Relation” which instructed them to remember the relative vertical relationship of the two circles, using the red-center as the reference. At test, participants indicated whether the test circles had the same relationship or not.
Mentions: As shown in Figure 1, all stimuli were presented on a 50% gray background. A trial began with a 1000 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”). This task cue was followed by a 200 ms arrow cue, which indicated whether the left or right hemifield should be attended. A sample array was then presented for 500 ms, which contained four circles of varying shades of gray (each subtending 0.3° of visual angle), 2 in each hemifield. One circle in each hemifield contained a red center (0.1°). After a 8 s delay period, four more circles, two in each hemifield, were presented as the test array for 1500 ms during which the participant entered a response. The test array was followed by a 200 ms feedback period where the fixation cross turned green for a correct response, red for an incorrect response, and blue if the response was slower than 1500 ms. After every 10 trials, the word “REST” was presented in the center of the screen for 12 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.