Chapter 31 Neural correlates of phosphene perception

Meister, Ingo G.; Weidemann, Juergen; Dambeck, Nina; Foltys, Henrik; Sparing, Roland; Krings, Timo; Thron, A.; Boroojerdi, Babak

doi:10.1016/s1567-424x(09)70234-x

Cited by 10 publications

(9 citation statements)

References 21 publications

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“…Four subjects were unable to perceive phosphenes even at maximum stimulator output. Such a failure rate is in accordance with previous studies of phosphene elicitation (22,29,30). However, all subjects who were not able to perceive phosphenes had a MT in the normal range.…”

Section: Subjectssupporting

confidence: 91%

“…Interestingly, the S-R curves of both cortexes, V1 and M1, showed a similar pattern with more prominent effects of HV at lower stimulation intensities. However, we cannot exclude the possibility that HV produces changes of V1 excitability by acting on subcortical pathways since the exact anatomic origin of phosphene generation is still unknown (22). Previous results, which have found that HV shortened the latency of visual-evoked potentials in demyelinating disease (2, 9), support the view that axonal effects underlie the effect reported here.…”

Section: Effects Of Hv On Visual Cortex Excitabilitysupporting

confidence: 52%

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Excitability of human motor and visual cortex before, during, and after hyperventilation

Sparing¹,

Dafotakis²,

Buelte³

et al. 2007

Journal of Applied Physiology

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Sparing R, Dafotakis M, Buelte D, Meister IG, Noth J. Excitability of human motor and visual cortex before, during, and after hyperventilation. J Appl Physiol 102: 406 -411, 2007. First published September 21, 2006; doi:10.1152/japplphysiol.00770.2006.-In humans, hyperventilation (HV) has various effects on systemic physiology and, in particular, on neuronal excitability and synaptic transmission. However, it is far from clear how the effects of HV are mediated at the cortical level. In this study we investigated the effects of HV-induced hypocapnia on primary motor (M1) and visual cortex (V1) excitability. We used 1) motor threshold (MT) and phosphene threshold (PT) and 2) stimulus-response (S-R) curves (i.e., recruitment curves) as measures of excitability. In the motor cortex, we additionally investigated 3) the intrinsic inhibitory and facilitatory neuronal circuits using a short-interval paired-pulse paradigm. Measurements were performed before, during, and after 10 min of HV (resulting in a minimum end-tidal PCO2 of 15 Torr). HV significantly increased motor-evoked potential (MEP) amplitudes, particularly at lower transcranial magnetic stimulation (TMS) intensities. Pairedpulse stimulation indicated that HV decreases intracortical inhibition (ICI) without changing intracortical facilitation. The results suggest that low PCO 2 levels modulate, in particular, the intrinsic neuronal circuits of ICI, which are largely mediated by neurons containing ␥-aminobutyric acid. Modulation of MT probably resulted from alterations of Na ϩ channel conductances. A significant decrease of PT, together with higher intensity of phosphenes at low stimulus intensities, furthermore suggested that HV acts on the excitability of M1 and V1 in a comparable fashion. This finding implies that HV also affects other brain structures besides the corticospinal motor system. The further exploration of these physiological mechanisms may contribute to the understanding of the various HV-related clinical phenomenona. partial pressure of carbon dioxide; phosphenes; threshold; pairedpulse transcranial magnetic stimulation; intracortical facilitation; intracortical inhibition HYPERVENTILATION (HV) (or hyperpnea) is the state of breathing faster or deeper than necessary, thereby reducing the CO 2 concentration of the blood below normal. What is usually referred to as HV is, in fact, hypocapnia. Since a reduction of arterial PCO 2 (Pa CO 2 ) below the normal level (40 Torr) is obtained by increasing the alveolar ventilation, HV became synonymous with hypocapnia (32). HV is known to have various effects on human physiology (for a review, see Ref. 6).For instance, a reduction in Pa CO 2 increases the excitability of sensory and motor axons in the peripheral nervous system (21,23,28).The aim of the present study was to investigate further the neural mechanisms of the HV-induced changes in cortical excitability. As measures of primary motor cortex (M1) excitability, motor threshold (MT), stimulus-response (S-R) curves (i.e., recruitment curves), intra...

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Section: Subjectssupporting

confidence: 91%

Section: Effects Of Hv On Visual Cortex Excitabilitysupporting

confidence: 52%

Excitability of human motor and visual cortex before, during, and after hyperventilation

Sparing¹,

Dafotakis²,

Buelte³

et al. 2007

Journal of Applied Physiology

Self Cite

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“…Specifically, fMRI activation has been found to differ during visual checkerboard stimulation (Meister et al 2003) as well as TMS (Caparelli et al 2010) for participants that do not report phosphenes. However, Caparelli et al (2010) observed TMS-related blood oxygenation-level-dependent signal changes in both types of participants.…”

Section: Discussionmentioning

confidence: 99%

Mapping the visual brain areas susceptible to phosphene induction through brain stimulation

Schaeffner

Welchman

2016

Exp Brain Res

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Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique whose effects on neural activity can be uncertain. Within the visual cortex, phosphenes are a useful marker of TMS: They indicate the induction of neural activation that propagates and creates a conscious percept. However, we currently do not know how susceptible different areas of the visual cortex are to TMS-induced phosphenes. In this study, we systematically map out locations in the visual cortex where stimulation triggered phosphenes. We relate this to the retinotopic organization and the location of object- and motion-selective areas, identified by functional magnetic resonance imaging (fMRI) measurements. Our results show that TMS can reliably induce phosphenes in early (V1, V2d, and V2v) and dorsal (V3d and V3a) visual areas close to the interhemispheric cleft. However, phosphenes are less likely in more lateral locations (hMT+/V5 and LOC). This suggests that early and dorsal visual areas are particularly amenable to TMS and that TMS can be used to probe the functional role of these areas.

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“…Apparently, phosphenes are generated in V1, the primary visual cortex, and V2/3, the extrastriate visual-cortical areas [2, 5,6], indicating that the primary visual cortex is one fundamental area for phosphene perception [7,8]; nevertheless, others studies point to its subcortical origin (e.g., optic radiation) [9]. Meister and colleagues [10] found remarkable differences in fMRI-activation during visual stimulation (checkerboard paradigm) between people perceiving phosphene and those lacking this perception, suggesting that this disparity might reflect inter-individual functional differences in visual neuronal networks. To verify this supposition, we interleaved TMS pulses in occipital cortices and 4-Tesla whole-brain blood oxygenation level dependent (BOLD)-fMRI acquisition to image local and distant co-activations, and reveal their association with phosphene generation.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous TMS-fMRI of the Visual Cortex Reveals Functional Network, Even in Absence of Phosphene Sensation

Ec¹,

Backus²,

Telang³

et al. 2010

Open Neuroimag J

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Phosphene sensation is commonly used to measure cortical excitability during transcranial magnetic stimulation (TMS) of the occipital cortex. However, some individuals lack this perception, and the reason for it is still unknown. In this work, we used functional magnetic resonance imaging (fMRI) to detect brain activation during local TMS of the occipital cortex in twelve healthy subjects. We found that TMS modulated brain activity in areas connected to the stimulation site, even in people unable to see phosphene. However, we observed a trend for a lower blood-oxygenation-level dependent (BOLD) signal, and smaller brain-activation clusters near the stimulated site than in the interconnected brain areas, suggesting that TMS pulse is more effective downstream than at its application site. Furthermore, we noted prominent differences in brain activation/deactivation patterns between subjects who perceived phosphene and those who did not, implying a functional distinction in their neuronal networks that might explain the origin of differences in phosphene generation.

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Chapter 31 Neural correlates of phosphene perception

Cited by 10 publications

References 21 publications

Excitability of human motor and visual cortex before, during, and after hyperventilation

Excitability of human motor and visual cortex before, during, and after hyperventilation

Mapping the visual brain areas susceptible to phosphene induction through brain stimulation

Simultaneous TMS-fMRI of the Visual Cortex Reveals Functional Network, Even in Absence of Phosphene Sensation

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