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The impact of early visual cortex transcranial magnetic stimulation on visual working memory precision and guess rate

View Article: PubMed Central - PubMed

ABSTRACT

Neuroimaging studies have demonstrated that activity patterns in early visual areas predict stimulus properties actively maintained in visual working memory. Yet, the mechanisms by which such information is represented remain largely unknown. In this study, observers remembered the orientations of 4 briefly presented gratings, one in each quadrant of the visual field. A 10Hz Transcranial Magnetic Stimulation (TMS) triplet was applied directly at stimulus offset, or midway through a 2-second delay, targeting early visual cortex corresponding retinotopically to a sample item in the lower hemifield. Memory for one of the four gratings was probed at random, and participants reported this orientation via method of adjustment. Recall errors were smaller when the visual field location targeted by TMS overlapped with that of the cued memory item, compared to errors for stimuli probed diagonally to TMS. This implied topographic storage of orientation information, and a memory-enhancing effect at the targeted location. Furthermore, early pulses impaired performance at all four locations, compared to late pulses. Next, response errors were fit empirically using a mixture model to characterize memory precision and guess rates. Memory was more precise for items proximal to the pulse location, irrespective of pulse timing. Guesses were more probable with early TMS pulses, regardless of stimulus location. Thus, while TMS administered at the offset of the stimulus array might disrupt early-phase consolidation in a non-topographic manner, TMS also boosts the precise representation of an item at its targeted retinotopic location, possibly by increasing attentional resources or by injecting a beneficial amount of noise.

No MeSH data available.


Related in: MedlinePlus

Trial sequence and relative locations.(A) Participants viewed a sample array with 4 randomly chosen orientations, and remembered these over a two-second delay. During the delay participants received 3 pulses of real or sham TMS over their left or right hemisphere. The pulses happened either directly at the offset of the sample array, or midway during the delay. A cue array indicated which of the four orientations was probed for recall, and after a short blank, participants rotated a test grating via button presses to match the cued orientation. (B) Responses at the four visual field locations were analyzed according to their position relative to the pulse. The visual field position targeted by the pulse could overlap with the memory item that was cued (‘same’), the cued item could be contralateral to the affected visual field location (‘contra’), it could be ipsilateral to it (‘ipsi’), or diagonal to it (‘diagonal’). In the example depicted here, right early visual cortex is stimulated, targeting the lower-left visual field. Consequently, the upper left position becomes ‘ipsi’, the upper right position ‘diagonal’, the lower left ‘same’, and the lower right position ‘contra’–relative to the visual field location affected by the TMS pulse.
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pone.0175230.g001: Trial sequence and relative locations.(A) Participants viewed a sample array with 4 randomly chosen orientations, and remembered these over a two-second delay. During the delay participants received 3 pulses of real or sham TMS over their left or right hemisphere. The pulses happened either directly at the offset of the sample array, or midway during the delay. A cue array indicated which of the four orientations was probed for recall, and after a short blank, participants rotated a test grating via button presses to match the cued orientation. (B) Responses at the four visual field locations were analyzed according to their position relative to the pulse. The visual field position targeted by the pulse could overlap with the memory item that was cued (‘same’), the cued item could be contralateral to the affected visual field location (‘contra’), it could be ipsilateral to it (‘ipsi’), or diagonal to it (‘diagonal’). In the example depicted here, right early visual cortex is stimulated, targeting the lower-left visual field. Consequently, the upper left position becomes ‘ipsi’, the upper right position ‘diagonal’, the lower left ‘same’, and the lower right position ‘contra’–relative to the visual field location affected by the TMS pulse.

Mentions: We combined functional and anatomical MRI with neuro-navigated TMS during a psychophysical working memory task (Fig 1A). Neuroimaging was utilized for the purpose of neuro-navigation [43], allowing stable TMS stimulation sites across multiple psychophysical sessions. During the first (fMRI) session, anatomical and functional localizer data were obtained. The second (TMS) session determined the exact TMS target points (based on individually localized visual cortical activity; S1 Fig; S1 Movie) and TMS intensities to be used throughout the experiment. Participants also practiced 160 trials of the working memory task.


The impact of early visual cortex transcranial magnetic stimulation on visual working memory precision and guess rate
Trial sequence and relative locations.(A) Participants viewed a sample array with 4 randomly chosen orientations, and remembered these over a two-second delay. During the delay participants received 3 pulses of real or sham TMS over their left or right hemisphere. The pulses happened either directly at the offset of the sample array, or midway during the delay. A cue array indicated which of the four orientations was probed for recall, and after a short blank, participants rotated a test grating via button presses to match the cued orientation. (B) Responses at the four visual field locations were analyzed according to their position relative to the pulse. The visual field position targeted by the pulse could overlap with the memory item that was cued (‘same’), the cued item could be contralateral to the affected visual field location (‘contra’), it could be ipsilateral to it (‘ipsi’), or diagonal to it (‘diagonal’). In the example depicted here, right early visual cortex is stimulated, targeting the lower-left visual field. Consequently, the upper left position becomes ‘ipsi’, the upper right position ‘diagonal’, the lower left ‘same’, and the lower right position ‘contra’–relative to the visual field location affected by the TMS pulse.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383271&req=5

pone.0175230.g001: Trial sequence and relative locations.(A) Participants viewed a sample array with 4 randomly chosen orientations, and remembered these over a two-second delay. During the delay participants received 3 pulses of real or sham TMS over their left or right hemisphere. The pulses happened either directly at the offset of the sample array, or midway during the delay. A cue array indicated which of the four orientations was probed for recall, and after a short blank, participants rotated a test grating via button presses to match the cued orientation. (B) Responses at the four visual field locations were analyzed according to their position relative to the pulse. The visual field position targeted by the pulse could overlap with the memory item that was cued (‘same’), the cued item could be contralateral to the affected visual field location (‘contra’), it could be ipsilateral to it (‘ipsi’), or diagonal to it (‘diagonal’). In the example depicted here, right early visual cortex is stimulated, targeting the lower-left visual field. Consequently, the upper left position becomes ‘ipsi’, the upper right position ‘diagonal’, the lower left ‘same’, and the lower right position ‘contra’–relative to the visual field location affected by the TMS pulse.
Mentions: We combined functional and anatomical MRI with neuro-navigated TMS during a psychophysical working memory task (Fig 1A). Neuroimaging was utilized for the purpose of neuro-navigation [43], allowing stable TMS stimulation sites across multiple psychophysical sessions. During the first (fMRI) session, anatomical and functional localizer data were obtained. The second (TMS) session determined the exact TMS target points (based on individually localized visual cortical activity; S1 Fig; S1 Movie) and TMS intensities to be used throughout the experiment. Participants also practiced 160 trials of the working memory task.

View Article: PubMed Central - PubMed

ABSTRACT

Neuroimaging studies have demonstrated that activity patterns in early visual areas predict stimulus properties actively maintained in visual working memory. Yet, the mechanisms by which such information is represented remain largely unknown. In this study, observers remembered the orientations of 4 briefly presented gratings, one in each quadrant of the visual field. A 10Hz Transcranial Magnetic Stimulation (TMS) triplet was applied directly at stimulus offset, or midway through a 2-second delay, targeting early visual cortex corresponding retinotopically to a sample item in the lower hemifield. Memory for one of the four gratings was probed at random, and participants reported this orientation via method of adjustment. Recall errors were smaller when the visual field location targeted by TMS overlapped with that of the cued memory item, compared to errors for stimuli probed diagonally to TMS. This implied topographic storage of orientation information, and a memory-enhancing effect at the targeted location. Furthermore, early pulses impaired performance at all four locations, compared to late pulses. Next, response errors were fit empirically using a mixture model to characterize memory precision and guess rates. Memory was more precise for items proximal to the pulse location, irrespective of pulse timing. Guesses were more probable with early TMS pulses, regardless of stimulus location. Thus, while TMS administered at the offset of the stimulus array might disrupt early-phase consolidation in a non-topographic manner, TMS also boosts the precise representation of an item at its targeted retinotopic location, possibly by increasing attentional resources or by injecting a beneficial amount of noise.

No MeSH data available.


Related in: MedlinePlus