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Separate attentional components modulate early visual cortex excitability
Accepted Manuscript Separate attentional components modulate early visual cortex excitability Qadeer Arshad, Yuliya Nigmatullina, Vamsee Bhrugubanda, Paladd Asavarut, Pawel Obrocki, Adolfo M. Bronstein, R. Edward Roberts PII:
S0010-9452(13)00218-9
DOI:
10.1016/j.cortex.2013.08.016
Reference:
CORTEX 1069
To appear in:
CORTEX
Received Date: 18 June 2013 Revised Date:
25 July 2013
Accepted Date: 28 August 2013
Please cite this article as: Arshad Q, Nigmatullina Y, Bhrugubanda V, Asavarut P, Obrocki P, Bronstein AM, Roberts RE, Separate attentional components modulate early visual cortex excitability, CORTEX (2013), doi: 10.1016/j.cortex.2013.08.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Separate attentional components modulate early visual cortex excitability
Qadeer Arshad*, Yuliya Nigmatullina*, Vamsee Bhrugubanda, Paladd Asavarut, Pawel Obrocki, Adolfo M. Bronstein, R. Edward Roberts
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(*Both authors have equal contributions)
Academic Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, Fulham Palace Road, London, W6 8RF.
Corresponding author: R.E. Roberts [email protected]
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Disruption of the right lateralised fronto-parietal attentional network using neuro-modulation techniques has been shown to induce both functional and perceptual modulation of early visual cortex (Silvanto et al., 2009). Such modulation is suggested to be mediated by interhemispheric competition (Silvanto et al., 2009). To date in neurologically normal subjects no behavioural demonstration of such modulation exists. In this study, we stimulated the vestibular system during performance of an attentional task. A previous study has demonstrated that passive rotation combined with performance of a visual attentional task results in asymmetric modulation of the brainstem mediated vestibulo-ocular reflex (VOR) (Arshad et al., 2013). The modulation of the VOR is suggested to occur as a result of activating overlapping cortical networks responsible for processing both vestibular information and the attentional task in the right parietal lobe (Corbetta and Shulman, 2002; Dieterich et al., 2003; Miller et al., 2000; van Elk and Blanke, 2012), resulting in inhibition of the left hemisphere via interhemispheric competition (Arshad et al., 2013; Miller et al., 2000). This hypothesis was directly tested in a recent study where transcranial direct current stimulation of the parietal cortex was employed to assess the effect upon the VOR (Arshad et al., in press), with the largest modulation of the VOR observed during cathodal stimulation of left parietal cortex. Thus in this study, we combined caloric stimulation with a visual attention task to disrupt parietal interhemispheric balance in normal subjects, and measured the possible effect on V1/V2 excitability. Moreover, for the first time we delineate the specific contributions of spatial versus non-spatial attentional networks in modulating early visual cortex.
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We assessed V1 excitability using phosphenes, elicited by briefly stimulating the visual cortex using single pulse transcranial magnetic stimulation (TMS), with the intensity required to elicit a phosphene reflecting the underlying cortical excitability (Marg and Rudiak, 1994). Eighteen righthanded participants (male 14, mean age = 24; range 20-33) gave written informed consent as approved by the local research ethics committee. Subjects were blindfolded and were seated on a chair fitted with a fixed magnetic coil and head restraint system. The head was inclined 30 degrees from the horizontal plane for maximal horizontal canal caloric stimulation. Firstly, V1 stimulation site was localised using a functional method by placing the coil centrally over the inion then moving it dorsally until the brightest stationary phosphene percept is observed in the centre of the visual field (Walsh et al., 2003). Secondly, the threshold was established according to a modified binary staircase algorithm (Tyrrell and Owens, 1988) previously described (Seemungal et al., 2013). Subjects were trained to rate the intensity of the perceived phosphene on a scale from 0 (no phosphene, below threshold) to 5 (maximum brightness, 100% max stimulator output). We then used the established clinical approach for cold water (30oC) caloric irrigation (left or right ear, randomised order) for 40s to activate the vestibular system. The irrigations were separated by a period of 5 minutes to allow for any after effects to subside. Following each irrigation we immediately measured visual cortical excitability using 20 single TMS pulses (Guzman-Lopez et al., 2011) applied at 20% above phosphene threshold for each individual, with each pulse separated by 3s. Subjects responded verbally and rated each phosphene on a scale (0-5) based on the intensity of the perceived phosphene. The intensity of phosphenes was similar (not significantly different, p> 0.05 paired t-test) following either right or left ear caloric irrigation. 2
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We then examined whether performing a visuo-spatial attention task during vestibular activation would modulate V1 excitability. We repeated the procedure described above (i.e. caloric + TMS), however this time participants were given six numbers and their location on a 3X3 grid (Brooks matrix) to remember. The numbers were presented at the start of the trial during the caloric, and participants were then required to recall the numbers at the end of trial (Figure 1A). Participants were required to recall at least 4 out of 6 numbers in the correct position on the grid (mean correct= 4.9, STD=0.93). All subjects met the minimum criterion set. We found that the intensity of phosphenes was significantly reduced only when participants performed the visuo-spatial task during right ear caloric. In a repeated measures ANOVA, factors Caloric side (left, right), Task (visuospatial, no task) and Epoch (early: first 10 responses, late: second 10 responses), there was a significant Caloric side x Task interaction (F[1,8] = 7.05; p = 0.029) and Task x Epoch interaction (F[1,8]=5.58; p=0.046). Post hoc paired t-tests indicate that the effect was specific to the first epoch (t=3.59, p<0.007), thus the effect lasted around 30s and likely reflects the period of peak vestibular activation following the caloric (Figure 1B). We then explored whether behavioural performance on the task was related to phosphene perception, however we found no significant correlation between mean phosphene intensity and behaviour in the first epoch (r=0.1, p=0.81) or second epoch (r=0.2, p=0.63), but this might reflect the small group size and limited variability in behavioural performance allowed by the task. However, following left caloric no significant changes were observed in V1 excitability (p=0.23), Figure 1B); nor during a condition using a low load visuo-spatial attentional task where participants were required to remember only 3 numbers (p=0.72).
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To test whether this effect could be simply explained by an increase in cognitive load, we repeated the experiment in a separate group of 9 subjects using a non-visuo spatial task. Here participants were required to remember a string of seven numbers using a modified digit span (mean correct=6.1, STD=0.78). All subjects met the minimum requirement of remembering at least 5 out of the 7 numbers and furthermore this task has been used previously as it carries a relatively equivalent attentional load to the visuospatial task used here (Arshad et al., 2013). We analysed performance using the same ANOVA approach described above, but this revealed no significant interactions or effect of task performance on phosphene perception (p=0.6).
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We then directly compared the change in phosphene perception from baseline during task performance for each task (spatial or non-spatial), and found a significant effect of visuo-spatial task on perception of phosphenes during right caloric stimulation (t=2.6, p=0.019). We provide a novel behavioural demonstration that modulation of visual cortical excitability presents only during the specific interaction of a visuo-spatial task and right ear caloric. It has been previously shown that the interaction between visuo-spatial task during vestibular activation results in disruption of parietal balance as evidenced by the failure of vestibular cortical processing of the rightwards slow phase vestibular nystagmus (i.e. right cold caloric)(Arshad et al., 2013). Herein we show that disrupting parietal balance using the above interaction modulates the early visual cortex. Another novel aspect of the findings reported herein is that we are able to separate the attentional component of the visual cortex modulation by showing that specifically visuo-spatial attention (but not non-spatial attention) provides the modulatory effect. We propose that the cortical networks 3
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subserving specifically visuo-spatial attention and the central velocity storage mechanism (required to prolong the vestibular nystagmus) overlap (Arshad et al., 2013; Ventre-Dominey et al., 2003) in the right fronto-parietal attentional network (Corbetta and Shulman, 2002; Dieterich et al., 2003). This results in disruption of the normal parietal interhemispheric balance and leads to top down modulation (Silvanto et al., 2009; Sparing et al., 2009).
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In summary our findings provide the first behavioural demonstration that the parietal lobe modulates the early visual cortex, that this modulation is specific to visuo-spatial attention and subject to disruption of interhemispheric parietal balance.
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References: Arshad Q, Nigmatullina Y, and Bronstein AM. Handedness-Related Cortical Modulation of the Vestibular-Ocular Reflex. J Neurosci, 33 (7): 3221–3227, 2013.
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Arshad Q, Nigmatullina Y, Roberts RE, Bhrugubanda V, Asavarut P, Bronstein AM. Left Cathodal trans-cranial direct current stimulation of the parietal cortex leads to an asymmetrical modulation of the vestibular-ocular reflex. Brain Stimul. In press. Corbetta M and Shulman GL. Control of goal-directed and stimulus-driven attention in the brain. Nat Rev Neurosci, 3 (3): 215–229, 2002.
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Dieterich M, Bense S, Lutz S, Drzezga A, Stephan T, Bartenstein P, and Brandt T. Dominance for vestibular cortical function in the non-dominant hemisphere. Cereb Cortex, 13 (9): 994–1007, 2003.
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Guzman-Lopez J, Silvanto J, and Seemungal BM. Visual motion adaptation increases the susceptibility of area V5/MT to phosphene induction by transcranial magnetic stimulation. Clin Neurophysiol, 122 (10): 1951–1955, 2011. Marg E and Rudiak D. Phosphenes induced by magnetic stimulation over the occipital brain: description and probable site of stimulation. Optom Vis Sci, 71 (5): 301–311, 1994. Miller SM, Liu GB, Ngo TT, Hooper G, Riek S, Carson RG, and Pettigrew JD. Interhemispheric switching mediates perceptual rivalry. Curr Biol, 10 (7): 383, 2000.
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Seemungal BM, Guzman-Lopez J, Arshad Q, Schultz SR, Walsh V, and Yousif N. Vestibular Activation Differentially Modulates Human Early Visual Cortex and V5/MT Excitability and Response Entropy. Cereb Cortex, (23(1)): 12–9, 2013. Silvanto J, Muggleton N, Lavie N, and Walsh V. The perceptual and functional consequences of parietal top-down modulation on the visual cortex. Cereb Cortex, 19 (2): 327–330, 2009.
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Sparing R, Thimm M, Hesse MD, Küst J, Karbe H, and Fink GR. Bidirectional alterations of interhemispheric parietal balance by non-invasive cortical stimulation. Brain, 132 (11): 3011–3020, 2009.
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Tyrrell RA and Owens DA. A rapid technique to assess the resting states of the eyes and other threshold phenomena: the modified binary search (MOBS). Behavior Research Methods, Instruments, & Computers, 20 (2): 137–141, 1988. Van Elk M and Blanke O. Balancing bistable perception during self-motion. Exp Brain Res, 222 (3): 219–228, 2012. Ventre-Dominey J, Nighoghossian N, and Denise P. Evidence for interacting cortical control of vestibular function and spatial representation in man. Neuropsychol, 41 (14): 1884–1898, 2003. Walsh V, Pascual-Leone A, and Kosslyn SM. Transcranial magnetic stimulation: A neurochronometrics of mind. MIT press Cambridge, MA, 2003.
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Figure 1 (A) The experimental protocol; the caloric was applied for 40 seconds at which time either the spatial or non-spatial task was given to the subject. The first TMS pulse coincided with the end of the irrigation at 40 seconds. In total 20 pulses were delivered, separated by 3 seconds. The TMS was applied for a total duration of 60 seconds, divided into two time epochs; each representing 30 seconds (early and late). These epochs represent the decaying caloric-induced oculomotor response (red curved line). (B) Visual cortical excitability following right ear or left ear caloric (black solid line). Visual cortical excitability following concurrent vestibular activation and visuo-spatial attentional task for left or right ear are shown in by the red dashed line. (B insert right-hand side) The mean time course of the effect with standard errors in 6 second bins to illustrate the temporal dynamics of the modulation.
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S0010-9452(13)00218-9
DOI:
10.1016/j.cortex.2013.08.016
Reference:
CORTEX 1069
To appear in:
CORTEX
Received Date: 18 June 2013 Revised Date:
25 July 2013
Accepted Date: 28 August 2013
Please cite this article as: Arshad Q, Nigmatullina Y, Bhrugubanda V, Asavarut P, Obrocki P, Bronstein AM, Roberts RE, Separate attentional components modulate early visual cortex excitability, CORTEX (2013), doi: 10.1016/j.cortex.2013.08.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
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Separate attentional components modulate early visual cortex excitability
Qadeer Arshad*, Yuliya Nigmatullina*, Vamsee Bhrugubanda, Paladd Asavarut, Pawel Obrocki, Adolfo M. Bronstein, R. Edward Roberts
M AN U
SC
(*Both authors have equal contributions)
Academic Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, Fulham Palace Road, London, W6 8RF.
Corresponding author: R.E. Roberts [email protected]
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Disruption of the right lateralised fronto-parietal attentional network using neuro-modulation techniques has been shown to induce both functional and perceptual modulation of early visual cortex (Silvanto et al., 2009). Such modulation is suggested to be mediated by interhemispheric competition (Silvanto et al., 2009). To date in neurologically normal subjects no behavioural demonstration of such modulation exists. In this study, we stimulated the vestibular system during performance of an attentional task. A previous study has demonstrated that passive rotation combined with performance of a visual attentional task results in asymmetric modulation of the brainstem mediated vestibulo-ocular reflex (VOR) (Arshad et al., 2013). The modulation of the VOR is suggested to occur as a result of activating overlapping cortical networks responsible for processing both vestibular information and the attentional task in the right parietal lobe (Corbetta and Shulman, 2002; Dieterich et al., 2003; Miller et al., 2000; van Elk and Blanke, 2012), resulting in inhibition of the left hemisphere via interhemispheric competition (Arshad et al., 2013; Miller et al., 2000). This hypothesis was directly tested in a recent study where transcranial direct current stimulation of the parietal cortex was employed to assess the effect upon the VOR (Arshad et al., in press), with the largest modulation of the VOR observed during cathodal stimulation of left parietal cortex. Thus in this study, we combined caloric stimulation with a visual attention task to disrupt parietal interhemispheric balance in normal subjects, and measured the possible effect on V1/V2 excitability. Moreover, for the first time we delineate the specific contributions of spatial versus non-spatial attentional networks in modulating early visual cortex.
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We assessed V1 excitability using phosphenes, elicited by briefly stimulating the visual cortex using single pulse transcranial magnetic stimulation (TMS), with the intensity required to elicit a phosphene reflecting the underlying cortical excitability (Marg and Rudiak, 1994). Eighteen righthanded participants (male 14, mean age = 24; range 20-33) gave written informed consent as approved by the local research ethics committee. Subjects were blindfolded and were seated on a chair fitted with a fixed magnetic coil and head restraint system. The head was inclined 30 degrees from the horizontal plane for maximal horizontal canal caloric stimulation. Firstly, V1 stimulation site was localised using a functional method by placing the coil centrally over the inion then moving it dorsally until the brightest stationary phosphene percept is observed in the centre of the visual field (Walsh et al., 2003). Secondly, the threshold was established according to a modified binary staircase algorithm (Tyrrell and Owens, 1988) previously described (Seemungal et al., 2013). Subjects were trained to rate the intensity of the perceived phosphene on a scale from 0 (no phosphene, below threshold) to 5 (maximum brightness, 100% max stimulator output). We then used the established clinical approach for cold water (30oC) caloric irrigation (left or right ear, randomised order) for 40s to activate the vestibular system. The irrigations were separated by a period of 5 minutes to allow for any after effects to subside. Following each irrigation we immediately measured visual cortical excitability using 20 single TMS pulses (Guzman-Lopez et al., 2011) applied at 20% above phosphene threshold for each individual, with each pulse separated by 3s. Subjects responded verbally and rated each phosphene on a scale (0-5) based on the intensity of the perceived phosphene. The intensity of phosphenes was similar (not significantly different, p> 0.05 paired t-test) following either right or left ear caloric irrigation. 2
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We then examined whether performing a visuo-spatial attention task during vestibular activation would modulate V1 excitability. We repeated the procedure described above (i.e. caloric + TMS), however this time participants were given six numbers and their location on a 3X3 grid (Brooks matrix) to remember. The numbers were presented at the start of the trial during the caloric, and participants were then required to recall the numbers at the end of trial (Figure 1A). Participants were required to recall at least 4 out of 6 numbers in the correct position on the grid (mean correct= 4.9, STD=0.93). All subjects met the minimum criterion set. We found that the intensity of phosphenes was significantly reduced only when participants performed the visuo-spatial task during right ear caloric. In a repeated measures ANOVA, factors Caloric side (left, right), Task (visuospatial, no task) and Epoch (early: first 10 responses, late: second 10 responses), there was a significant Caloric side x Task interaction (F[1,8] = 7.05; p = 0.029) and Task x Epoch interaction (F[1,8]=5.58; p=0.046). Post hoc paired t-tests indicate that the effect was specific to the first epoch (t=3.59, p<0.007), thus the effect lasted around 30s and likely reflects the period of peak vestibular activation following the caloric (Figure 1B). We then explored whether behavioural performance on the task was related to phosphene perception, however we found no significant correlation between mean phosphene intensity and behaviour in the first epoch (r=0.1, p=0.81) or second epoch (r=0.2, p=0.63), but this might reflect the small group size and limited variability in behavioural performance allowed by the task. However, following left caloric no significant changes were observed in V1 excitability (p=0.23), Figure 1B); nor during a condition using a low load visuo-spatial attentional task where participants were required to remember only 3 numbers (p=0.72).
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To test whether this effect could be simply explained by an increase in cognitive load, we repeated the experiment in a separate group of 9 subjects using a non-visuo spatial task. Here participants were required to remember a string of seven numbers using a modified digit span (mean correct=6.1, STD=0.78). All subjects met the minimum requirement of remembering at least 5 out of the 7 numbers and furthermore this task has been used previously as it carries a relatively equivalent attentional load to the visuospatial task used here (Arshad et al., 2013). We analysed performance using the same ANOVA approach described above, but this revealed no significant interactions or effect of task performance on phosphene perception (p=0.6).
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We then directly compared the change in phosphene perception from baseline during task performance for each task (spatial or non-spatial), and found a significant effect of visuo-spatial task on perception of phosphenes during right caloric stimulation (t=2.6, p=0.019). We provide a novel behavioural demonstration that modulation of visual cortical excitability presents only during the specific interaction of a visuo-spatial task and right ear caloric. It has been previously shown that the interaction between visuo-spatial task during vestibular activation results in disruption of parietal balance as evidenced by the failure of vestibular cortical processing of the rightwards slow phase vestibular nystagmus (i.e. right cold caloric)(Arshad et al., 2013). Herein we show that disrupting parietal balance using the above interaction modulates the early visual cortex. Another novel aspect of the findings reported herein is that we are able to separate the attentional component of the visual cortex modulation by showing that specifically visuo-spatial attention (but not non-spatial attention) provides the modulatory effect. We propose that the cortical networks 3
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subserving specifically visuo-spatial attention and the central velocity storage mechanism (required to prolong the vestibular nystagmus) overlap (Arshad et al., 2013; Ventre-Dominey et al., 2003) in the right fronto-parietal attentional network (Corbetta and Shulman, 2002; Dieterich et al., 2003). This results in disruption of the normal parietal interhemispheric balance and leads to top down modulation (Silvanto et al., 2009; Sparing et al., 2009).
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In summary our findings provide the first behavioural demonstration that the parietal lobe modulates the early visual cortex, that this modulation is specific to visuo-spatial attention and subject to disruption of interhemispheric parietal balance.
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References: Arshad Q, Nigmatullina Y, and Bronstein AM. Handedness-Related Cortical Modulation of the Vestibular-Ocular Reflex. J Neurosci, 33 (7): 3221–3227, 2013.
RI PT
Arshad Q, Nigmatullina Y, Roberts RE, Bhrugubanda V, Asavarut P, Bronstein AM. Left Cathodal trans-cranial direct current stimulation of the parietal cortex leads to an asymmetrical modulation of the vestibular-ocular reflex. Brain Stimul. In press. Corbetta M and Shulman GL. Control of goal-directed and stimulus-driven attention in the brain. Nat Rev Neurosci, 3 (3): 215–229, 2002.
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Dieterich M, Bense S, Lutz S, Drzezga A, Stephan T, Bartenstein P, and Brandt T. Dominance for vestibular cortical function in the non-dominant hemisphere. Cereb Cortex, 13 (9): 994–1007, 2003.
M AN U
Guzman-Lopez J, Silvanto J, and Seemungal BM. Visual motion adaptation increases the susceptibility of area V5/MT to phosphene induction by transcranial magnetic stimulation. Clin Neurophysiol, 122 (10): 1951–1955, 2011. Marg E and Rudiak D. Phosphenes induced by magnetic stimulation over the occipital brain: description and probable site of stimulation. Optom Vis Sci, 71 (5): 301–311, 1994. Miller SM, Liu GB, Ngo TT, Hooper G, Riek S, Carson RG, and Pettigrew JD. Interhemispheric switching mediates perceptual rivalry. Curr Biol, 10 (7): 383, 2000.
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Seemungal BM, Guzman-Lopez J, Arshad Q, Schultz SR, Walsh V, and Yousif N. Vestibular Activation Differentially Modulates Human Early Visual Cortex and V5/MT Excitability and Response Entropy. Cereb Cortex, (23(1)): 12–9, 2013. Silvanto J, Muggleton N, Lavie N, and Walsh V. The perceptual and functional consequences of parietal top-down modulation on the visual cortex. Cereb Cortex, 19 (2): 327–330, 2009.
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Sparing R, Thimm M, Hesse MD, Küst J, Karbe H, and Fink GR. Bidirectional alterations of interhemispheric parietal balance by non-invasive cortical stimulation. Brain, 132 (11): 3011–3020, 2009.
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Tyrrell RA and Owens DA. A rapid technique to assess the resting states of the eyes and other threshold phenomena: the modified binary search (MOBS). Behavior Research Methods, Instruments, & Computers, 20 (2): 137–141, 1988. Van Elk M and Blanke O. Balancing bistable perception during self-motion. Exp Brain Res, 222 (3): 219–228, 2012. Ventre-Dominey J, Nighoghossian N, and Denise P. Evidence for interacting cortical control of vestibular function and spatial representation in man. Neuropsychol, 41 (14): 1884–1898, 2003. Walsh V, Pascual-Leone A, and Kosslyn SM. Transcranial magnetic stimulation: A neurochronometrics of mind. MIT press Cambridge, MA, 2003.
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Figure 1 (A) The experimental protocol; the caloric was applied for 40 seconds at which time either the spatial or non-spatial task was given to the subject. The first TMS pulse coincided with the end of the irrigation at 40 seconds. In total 20 pulses were delivered, separated by 3 seconds. The TMS was applied for a total duration of 60 seconds, divided into two time epochs; each representing 30 seconds (early and late). These epochs represent the decaying caloric-induced oculomotor response (red curved line). (B) Visual cortical excitability following right ear or left ear caloric (black solid line). Visual cortical excitability following concurrent vestibular activation and visuo-spatial attentional task for left or right ear are shown in by the red dashed line. (B insert right-hand side) The mean time course of the effect with standard errors in 6 second bins to illustrate the temporal dynamics of the modulation.
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