Figure 1.
On each trial subjects maintained fixation and indicated with a button press the perceived orientation of a Gabor pattern that was presented for 27 ms (static stimulus condition) or gradually increasing in contrast (reaction time experiment). For coarse orientation discrimination, subjects indicated whether the Gabor patterns appeared to be vertical or horizontal. For fine orientation discrimination, subjects indicated whether the Gabor pattern was oriented to the left or right of vertical.
Table 1.
Characteristics of experiments.
Figure 2.
Effects of theta-burst stimulation on coarse orientation discrimination.
Following stimulation of the primary visual cortex (dark gray bars), the percentage of correct orientation judgments increased by an average of 7.2 percent (left-most bar). Stimulation of the control site at the vertex of the scalp (light gray bars) did not on average improve performance.
Figure 3.
Stimulus and phosphene locations for the reaction-time task.
Coarse orientation discrimination was tested at nine locations in the visual field (open circles). Subjects fixated at the central point (black dot) as orientation discrimination was tested in each of the locations in order. Before stimulation, phosphenes were elicited in the right visual field. For the subjects that were able to report the specific location of the phosphene, they are marked by the small triangles and diamonds. All phosphenes were contralateral to stimulation and clustered around the horizontal meridian (location 5).
Figure 4.
Effects of rTMS across visual space for two subjects in each of the two stimulation (1 Hz and theta-burst) conditions applied to the occipital cortex (gray bars) or the vertex of the scalp (white bars).
Subjects were required to indicate whether a Gabor pattern was oriented horizontally or vertically, and the response time was taken as a measure of performance. Each panel shows the change in response time, which is represented as a z-score relative to the distribution of response times seen in pre-rTMS testing. Here positive numbers represent faster reaction times.
Figure 5.
Time-course of results in the reaction-time task.
Each panel shows the time course of results for the representative subjects in figure 4 following 1 Hz (left) or theta-burst (right) stimulation. For all subjects a modest but consistent improvement in both ipsilateral (blue) and contralateral (red) visual fields is closely related throughout the time course for both theta-burst and 1 Hz stimulation as compared to stimulation of the vertex of the scalp (black). The improvement persists beyond 60 minutes post stimulation.
Figure 6.
Results for the fine orientation discrimination task.
Subjects were required to indicate whether the orientation of a briefly-presented Gabor stimulus was to the left or right of vertical. The bars show the effects of continuous theta-burst stimulation of primary visual cortex on six subjects and for the mean (leftmost bar).
Figure 7.
Theoretical analysis of possible rTMS-induced changes in neuronal responses.
Each pixel in the map represents a change in signal-to-noise ratio (see text for mathematical definition) for a given change in firing rate (ordinate) or covariance in neuronal responses (abscissa). Larger signal-to-noise ratios are indicated by reddish colors, and smaller ratios are indicated by bluish colors. Although decreasing firing rates leads to poorer signal-to-noise ratio, such decreases can be compensated for by a corresponding decrease in covariance. The observed mean improvement in orientation discrimination following theta-burst stimulation (72.4% pre-TMS to 78.9%+/−3.6% post-TMS) corresponds to an 18%–53% improvement in signal-to-noise ratio (highlighted gray area).