Automatic representation of a visual stimulus relative to a background in the right precuneus

2017

Front. Syst. Neurosci.

A remembered saccade target could be encoded in egocentric coordinates such as gaze-centered, or relative to some external allocentric landmark that is independent of the target or gaze (landmark-centered). In comparison to egocentric mechanisms, very little is known about such a landmark-centered representation. Here, we used an event-related fMRI design to identify brain areas supporting these two types of spatial coding (i.e., landmark-centered vs. gaze-centered) for target memory during the Delay phase where only target location, not saccade direction, was specified. The paradigm included three tasks with identical display of visual stimuli but different auditory instructions: Landmark Saccade (remember target location relative to a visual landmark, independent of gaze), Control Saccade (remember original target location relative to gaze fixation, independent of the landmark), and a non-spatial control, Color Report (report target color). During the Delay phase, the Control and Landmark Saccade tasks activated overlapping areas in posterior parietal cortex (PPC) and frontal cortex as compared to the color control, but with higher activation in PPC for target coding in the Control Saccade task and higher activation in temporal and occipital cortex for target coding in Landmark Saccade task. Gaze-centered directional selectivity was observed in superior occipital gyrus and inferior occipital gyrus, whereas landmark-centered directional selectivity was observed in precuneus and midposterior intraparietal sulcus. During the Response phase after saccade direction was specified, the parietofrontal network in the left hemisphere showed higher activation for rightward than leftward saccades. Our results suggest that cortical activation for coding saccade target direction relative to a visual landmark differs from gaze-centered directional selectivity for target memory, from the mechanisms for other types of allocentric tasks, and from the directionally selective mechanisms for saccade planning and execution.

Section: Discussionmentioning

confidence: 77%

Cortical Activation during Landmark-Centered vs. Gaze-Centered Memory of Saccade Targets in the Human: An FMRI Study

2017

Front. Syst. Neurosci.

Section: Neural Mechanisms For Allo‐to‐ego Conversion Of Remembered Rmentioning

confidence: 99%

“…These findings revealed unknown roles played by these four areas in early visuospatial transformations of reach targets when an allocentric landmark is available to represent targets relative to it. This does not mean that they are exclusive for these functions: previous literature suggests that they likely perform multiple functions, including automatic coding of allocentric targets within large background, 74 egocentric transformations for reach control, 15,75,76 as well as general reach planning. [77][78][79][80][81][82] Functional overview of allocentric, egocentric, and allo-to-ego transformations for reach Figure 5A provides an overview of the cortical regions and their functional connectivity for allocentric and egocentric coding of target direction in memory, conversion of allocentric to egocentric target representations, and egocentric reach directional selectivity for planning and execution.…”

Section: Neural Mechanisms For Allo-to-ego Conversion Of Remembered Rmentioning

confidence: 99%

Allocentric representations for target memory and reaching in human cortex

Annals of the New York Academy of Sciences

2019

The use of allocentric cues for movement guidance is complex because it involves the integration of visual targets and independent landmarks and the conversion of this information into egocentric commands for action. Here, we focus on the mechanisms for encoding reach targets relative to visual landmarks in humans. First, we consider the behavioral results suggesting that both of these cues influence target memory, but are then transformed—at the first opportunity—into egocentric commands for action. We then consider the cortical mechanisms for these behaviors. We discuss different allocentric versus egocentric mechanisms for coding of target directional selectivity in memory (inferior temporal gyrus versus superior occipital gyrus) and distinguish these mechanisms from parieto‐frontal activation for planning egocentric direction of actual reach movements. Then, we consider where and how the former allocentric representations of remembered reach targets are converted into the latter egocentric plans. In particular, our recent neuroimaging study suggests that four areas in the parietal and frontal cortex (right precuneus, bilateral dorsal premotor cortex, and right presupplementary area) participate in this allo‐to‐ego conversion. Finally, we provide a functional overview describing how and why egocentric and landmark‐centered representations are segregated early in the visual system, but then reintegrated in the parieto‐frontal cortex for action.

“…Taken together, our results suggest that right pPrecuneus, right Pre-SMA and bilateral PMd are the best likely candidates for the Allo-Ego conversion in our tasks, although they likely also play other, more general functions in vision and reach planning. For example, precuneus has been observed to be active during other types of visual-motor dissociation tasks (Fernandez-Ruiz et al, 2007;Gertz & Fiehler, 2015;Gorbet & Sergio, 2016), and it was also implicated in the automatic coding of allocentric targets in large background coordinates (Uchimura et al, 2015) and processing spatial information for motor imagery (Cavanna & Trimble, 2006).…”

Section: Specific Areas Involved In the Allo-ego Conversionmentioning

confidence: 99%

Neural substrates for allocentric‐to‐egocentric conversion of remembered reach targets in humans

Monaco

2018

Eur J of Neuroscience

Targets for goal-directed action can be encoded in allocentric coordinates (relative to another visual landmark), but it is not known how these are converted into egocentric commands for action. Here, we investigated this using a slow event-related fMRI paradigm, based on our previous behavioural finding that the allocentric-to-egocentric (Allo-Ego) conversion for reach is performed at the first possible opportunity. Participants were asked to remember (and eventually reach towards) the location of a briefly presented target relative to another visual landmark. After a first memory delay, participants were forewarned by a verbal instruction if the landmark would reappear at the same location (potentially allowing them to plan a reach following the auditory cue before the second delay), or at a different location where they had to wait for the final landmark to be presented before response, and then reach towards the remembered target location. As predicted, participants showed landmark-centred directional selectivity in occipital-temporal cortex during the first memory delay, and only developed egocentric directional selectivity in occipital-parietal cortex during the second delay for the 'Same cue' task, and during response for the 'Different cue' task. We then compared cortical activation between these two tasks at the times when the Allo-Ego conversion occurred, and found common activation in right precuneus, right presupplementary area and bilateral dorsal premotor cortex. These results confirm that the brain converts allocentric codes to egocentric plans at the first possible opportunity, and identify the four most likely candidate sites specific to the Allo-Ego transformation for reaches.