Measurement of Human Visual Cortex Excitability using Suprathreshold Phosphene Perception
Alice
K.
Lagas1, 2*,
Cathy
M.
Stinear2, 3,
Winston
D.
Byblow2, 4,
Bruce
R.
Russel2, 5,
Robert
R.
Kydd2, 3 and
Benjamin
Thompson1, 2
-
1
University of Auckland, Optometry and Vision Science, New Zealand
-
2
University of Auckland, Centre for Brain Research, New Zealand
-
3
University of Auckland, School of Medicine, New Zealand
-
4
University of Auckland, Department of Sport and Exercise Science, New Zealand
-
5
University of Auckland, School of Pharmacy, New Zealand
Human visual cortex excitability can be measured by using single-pulse transcranial magnetic stimulation (TMS) to induce the percept of a phosphene. The standard technique involves varying the intensity of TMS delivered to the occipital pole, until an intensity that produces phosphenes on 50% of pulses is identified. Here we investigated the perception of phosphenes induced by single-pulse TMS delivered at varying suprathreshold intensities. The aim was to assess whether suprathreshold phosphene perception could provide an additional measure of visual cortex excitability. Seven healthy adult males completed measurements of threshold and suprathreshold phosphene perception on three separate occasions. Phosphene thresholds were determined using standard techniques. Perception of suprathreshold phosphenes was assessed with single-pulse TMS across a fixed range of five stimulator output strengths. Participants rated the intensity of each phosphene relative to the percept induced by the maximum TMS strength used within a session. A logistic function was fitted to the average intensity ratings which provided a 50% intensity threshold. Phosphene intensity ratings were correlated with phosphene thresholds (Pearson’s R = 0.84, p<0.02) and did not vary systematically across sessions, F(2,12) = 0.33, p=0.7. In contrast, phosphene thresholds declined significantly across sessions, possibly due to task learning F(2,12) = 6.18, p=0.014. These results suggest that measurements of suprathreshold phosphene perception may provide a useful additional measure of human visual cortex excitability.
Keywords:
phosphene perception,
Phosphenes,
TMS,
Visual Cortex,
phosphene threshold,
excitability,
Transcranial Magnetic Stimulation
Conference:
ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012.
Presentation Type:
Poster Presentation
Topic:
Sensation and Perception
Citation:
Lagas
AK,
Stinear
CM,
Byblow
WD,
Russel
BR,
Kydd
RR and
Thompson
B
(2012). Measurement of Human Visual Cortex Excitability using Suprathreshold Phosphene Perception.
Conference Abstract:
ACNS-2012 Australasian Cognitive Neuroscience Conference.
doi: 10.3389/conf.fnhum.2012.208.00156
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Received:
11 Oct 2012;
Published Online:
17 Nov 2012.
*
Correspondence:
Miss. Alice K Lagas, University of Auckland, Optometry and Vision Science, Auckland, Auckland, 1010, New Zealand, a.lagas@auckland.ac.nz