Neuromuscular Consequences of Reflexive Covert Orienting

Transcription

1 Neuromuscular Consequences of Reflexive Covert Orienting Brian D. Corneil, Douglas P. Munoz, Brendan B. Chapman, Tania Admans, Sharon L. Cushing Fixation Cue (3 ms) CTOA 5, 2 or 6 ms Fixation Target Supplementary Figure 1. The saccade cueing task, which is an oculomotor version of the Posner cueing task 1, with CTOAs selected to produce attention capture 2 and inhibition of return 3-6. In this task, monkeys are trained to maintain fixation during a briefly flashed visual cue, and subsequently look to the target which appeared simultaneously with disappearance of the fixation point.

2 Frequency of microsaccade occurrence Cue onset * * * * Target onset Toward Cue Away from Cue Time from Target presentation (ms) Supplementary Figure 2. The animals were trained to maintain central fixation while the fixation point remained illuminated, regardless of the side or timing of cue presentation. Is it possible that signals associated with reflexive covert orienting recruited extraocular eye muscles, but perhaps because of ocular biomechanics or co-contraction did not move the eyes? We deem these possibilities highly unlikely. Studies of extraocular muscle motoneurons recorded in awake animals have never described either visual transient responses resembling those described here, or provided any evidence of co-contraction Furthermore, the eyes are very responsive to small changes in muscle force 14,15, and we did not observe changes in eye position (> 1 ) following cue onset. Consistent with previous results in humans 16,17, we observed changes in the pattern of microsaccades (< 1 deg) as a result of cueing, however their overall frequency decreased in the 1-2 ms interval following cue onset, unlike neck EMG. To show this, we present the frequency and direction of microsaccades for 6 ms CTOA trials. Microsaccades were detected as small eye movements <1 deg in amplitude with peak velocities exceeding 2 deg/s. Data has been pooled across both monkeys and across all stimulus eccentricities and directions. The value of each histogram (bin width 5 ms) represents the frequency with which microsaccades occurred within the time interval. Upward oriented histograms represent the frequency of microsaccades directed toward the cue, and downward oriented histograms represent the frequency of microsaccades directed away from the cue. Asterisks denote bins within which there was a significantly biased direction of microsaccades (chi-square test, P <.5). Note how microsaccade direction is biased toward the cue ~1-2 ms after cue onset, but that the overall rate of microsaccade occurrence (either toward or away from the cue) during this interval is decreased compared to the bins preceding cue onset. Microsaccade direction is biased away from the cue ~35-45 ms following cue onset. While these data do show that microsaccade frequency and direction are biased in a cueing task, consistent with previous results 16,17, it bears emphasis that microsaccades occur on a minority of all trials, unlike changes in neck EMG. Furthermore, the timing of changes in microsaccade frequency lags the profiles of neck EMG reported in the main manuscript.

3 a 5 ms CTOA b 2 ms CTOA 8 RCP maj activity (µv) Contra 2 15 c 6 ms CTOA RCP maj activity (µv) 8 2 Contra SAME OPPOSITE CONTROL 15 SP cap activity (µv) SP cap activity (µv) d EMG RCP (µv) Time from Target presentation (ms) * SAME OPPOSITE CTOA (ms) e EMG RCP Difference (µv) CTOA (ms) Supplementary Figure 3. EMG activity recorded from bilateral rectus capitis posterior major (RCP maj) and right splenius capitis (SP cap) during the cueing task, taken from the same session as shown in Fig. 1 of the main manuscript (i.e., target presented 27deg right). Same format as Fig. 1 of the main manuscript. Recordings from left-sp cap were unsuccessful in both animals. Note how the patterns of EMG activity in bilateral RCP maj resemble those recorded from bilateral obliquus capitis inferior (OCI; see Fig. 1 of manuscript). Although a visual response in not apparent on ipsilateral (right) SP-cap, the activity of this muscle in response to target onset is still strongly modulated by cue location and CTOA (e.g., Supplementary Fig. 3b). Because SP-cap was recorded unilaterally, we only calculated the EMG metric for RCP maj (termed EMG RCP ). A two-way ANOVA of EMG RCP across CTOA and cue location demonstrated significant effects of cue location (P <.1) and an interaction between CTOA and cue location (P < 1-5 ). Asterisk denotes EMG observations that were significantly different at the 2 ms CTOA (Bonferronicorrected post-hoc t-test, P <.5).

4 a Normalized cue magnitude b Normalized plateau magnitude lateral Cue Contralateral Cue Cue Eccentricity (deg) Supplementary Figure 4. Influence of cue eccentricity on OCI responses. a. Normalized magnitude of cue response (relative to the response at 35 deg) plotted as a function of eccentricity. The magnitude of the visual response in OCI to the cue presented on the ipsilateral side increased with increasing eccentricity (Pearson's r =.25; P < 1-5 ; n = 7287 trials), whereas the magnitude of the visual response in contralateral OCI decreased with increasing eccentricity (Pearson's r = -.65; P < 1-5, n = 7347 trials). b. We also observed an increasing monotonic relationship between the magnitude of the post-cue plateau and cue eccentricity in the ipsilateral muscle (Pearson's r =.86; P < 1-4 ; n = 3656) but not the contralateral muscle (Pearson's r = -.12; P =.47; n = 3658; the postcue plateaus are normalized to the magnitude of the cue response at 35 deg). The lack of effect of the depression for contralateral EMG may be the result of a floor effect.

5 a 1 5 ms CTOA b 2 ms CTOA OCI activity (µv) Contra 3 OCI activity (µv) c 1 3 Contra 6 ms CTOA SAME OPPOSITE CONTROL Time from Target presentation (ms) d EMG (µv) 4 2 * SAME OPPOSITE CTOA (ms) e EMG Difference (µv) CTOA (ms) Supplementary Figure 5. EMG activity recorded from bilateral obliquus capitis inferior (OCI) during the cueing task, taken a session where the target was placed 1 deg to the right. Same format as Fig. 1 of the main manuscript. Note how the patterns of EMG activity in bilateral OCI resemble those recorded when the stimuli are placed at more eccentric positions, but are of a weaker magnitude. A two-way ANOVA of EMG across CTOA and cue location demonstrated a significant interaction effect between CTOA and cue location (P =.2). Asterisk denotes EMG observations that were significantly different at the 2 ms CTOA (Bonferroni-corrected, post-hoc t-test, P <.5).

6 a deg 15 deg 2 deg 27 deg 35 deg e 4 normalized EMG Difference 1 b 1 c 1 d CTOA (ms) 5 ms CTOA 2 ms CTOA 6 ms CTOA Target eccentricity (º) SRT Difference (ms) CTOA (ms) f 2 2 g 2 2 h ms CTOA 2 ms CTOA 6 ms CTOA Target eccentricity (º) Supplementary Figure 6. Influence of target eccentricity on differences in EMG (a-d) or SRT (e-h) for each CTOA employed. The EMG values are normalized to the value obtained at the 2 ms CTOA with the target placed at 35 deg (= -1). The top row in each column shows differences in EMG (a) or SRT (e) versus CTOA for 5 different target eccentricities. Note how the differences in EMG at the 2 ms CTOA scale with eccentricity, being largest for targets placed at 35 deg and smallest but still present for targets placed at 1 deg (see Supplementary Fig. 5 for figure and statistics for 1 deg data). The scaling with EMG with target eccentricity is consistent with increasing levels of neck muscle recruitment accompanying progressively larger gaze shifts 18,19. Note as well how the greatest EMG differences were consistently observed at the 2 ms CTOA, which also produced the greatest IOR on SRT. The bottom three rows in each column show the difference values as a function of target eccentricity, plotted separately for the 5, 2 and 6 ms CTOAs. A three-way ANOVA of the EMG value across CTOA, cue location, and target eccentricity revealed a significant effect of cue location (P <.1) and eccentricity (P < 1-5 ), a significant two-way interactions between CTOA and cue location (P < 1-5 ), cue location and eccentricity (P <.5), and a significant three-way interaction across all factors (P <.5). An equivalent three-way ANOVA of SRT revealed a significant effect of CTOA (P < 1-5 ), eccentricity (P < 1-5 ), and significant two-way interactions between CTOA and cue location (P < 1-5 ) and CTOA and eccentricity (P <.5).

7 a b.4 P < r-value r-value Frequency (%) c Frequency (%) Target eccentricity (º) RCP maj r = -.56 P <.5 P < r-value Supplementary Figure 7. Because the transient visual EMG responses occurred prior to the saccade, we sought to additionally determine whether the EMG metric would be a reliable predictor of the ensuing SRT on a given trial, as this may provide insights into the underlying neural mechanisms. To do this, we contrasted on a trial-by-trial basis the relationship between EMG and the ensuing SRT for each target location across all conditions (2 monkeys, 2 target directions, 5 target eccentricities for a total of 2 regressions). Overall, 17/2 of these relationships were characterized by a significantly negative correlation (Pearson's r < and P <.5). In a, we show the r-values from correlations of EMG responses to SRT. Filled bars represent correlations that were significant within a single block of trials (P <.5). This distribution was distributed significantly below zero (mean +/- s.d., r = , n = 2, one-tailed t-test vs. zero, P < 1-5 ). In b, we plot these r-values as a function of target eccentricity. Filled squares represent correlations that were significant within a single block of trials (P <.5). A linear regression of the r-values versus target eccentricity was significant (Pearson's r = -.56, P <.5, n = 2). In c, we plot r-values from correlations of EMG RCP responses to SRT. Filled bars represent correlations that were significant within a single block of trials (P <.5). This distribution was distributed significantly below zero (mean +/- s.d., r = -.7.1, n = 2, one-tailed t-test vs. zero, P <.1).

8 a 5 ms CTOA b 2 ms CTOA SAME OPPOSITE CONTROL 16 OCI activity (µv) Contra 4 3 Eye Eye Horizontal Velocity (deg/s) 3 3 Gaze Head Gaze Head Time from Target presentation (ms) Supplementary Figure 8. EMG activity and horizontal eye, head, and gaze velocity recorded for a target presented 27 deg to the right for the 5 and 2 ms CTOA, taken from the same session shown in Fig. 2 of the main manuscript. Upward deflections in these traces denote rightward movements. Note how the eyes and head move in opposite directions about 1-3 ms following cue presentation (most easily seen at the 2 ms CTOA). During this interval, the head moves toward the cue, but gaze remains stable due to compensatory VOR movements of the eyes in the opposite direction.

9 METHODS All experimental protocols were in accordance with the Canadian Council on Animal Care policy on the use of laboratory animals and approved by the Animal Use Subcommittee of the University of Western Ontario Council on Animal Care. Two male rhesus monkeys (Macaca mulatta) were prepared for chronic recording of eye and head position and neck EMG activity All analog data were digitized at 1 khz by a multichannel recording system [Plexon Inc; prior to digitization, EMG data were amplified (1x) and filtered (1Hz 4kHz)]. Offline, EMG signals were rectified and integrated into 1 ms bins. Behavioural task: All aspects of the experimental paradigm were controlled by a realtime controller (LabVIEW, National Instruments). Monkeys sat in a customized chair that restricted torso rotation to 1º, and faced an array of red light-emitting diodes, with their heads either restrained or unrestrained (in both monkeys, head-restrained experiments were conducted first). They were trained to perform a saccade cueing task 21 (Supplementary Fig. 1). Each trial began with the monkey fixating a central fixation spot for 5-1, ms, within a fixation window of 3 radius. A visual cue was then presented to either the left or right for 3 ms. Following a delay, the cue-target onset asynchrony (CTOA), a target appeared either to the left or right side and the monkeys were required to look to the target to receive a liquid reward. CTOA was varied pseudo-randomly between 5 ms, 2 ms, and 6 ms and the cue and target were equally likely to appear on the left or right side. No-cue CONTROL trials were randomly interleaved among the cueing trials. The eccentricity of the cue and target was fixed within a block of trials, and varied between 1, 15, 2, 27, and 35 across blocks of trials. Trials in which the

10 monkeys looked to the cue, or had saccade reaction times (SRT) less that 7 ms or greater than 5 ms were excluded from further analyses, as were trials with excessive amounts of neck EMG activity (e.g., due to postural adjustments). Data analysis: We analyzed how both SRT and neck EMG activity varied as a function of CTOA and cue location relative to the target (SAME or OPPOSITE). For the EMG data, we were interested in the time-locked neck EMG recruitment following target presentation 18. We first segregated all data by the side of target presentation, CTOA, and cue location, and smoothed the EMG data with a 9-point (9 ms) running average. We then determined when neck EMG discriminated the side of target presentation by calculating a receiver operating characteristic (ROC) curve every 1 ms sample between 1 ms before to 3 ms after target presentation 18. The area under the ROC curve represents the probability that an ideal observer could discern the side of target presentation given the neck EMG activity recorded over all trials at that sample. An area of.5 or 1. indicates that an ideal observer would operate at chance or perform perfectly, respectively. We defined the discrimination time (the time at which neck EMG activity informed about target location) as the time after target presentation when the ROC area surpassed a value of.6 for at least 1 of the next 15 samples. This.6 level corresponds to the upper 95% confidence interval of random ROC values arrived at by using a bootstrap analysis (5 iterations randomly assigning EMG activity to left or right target presentation) of the EMG activity from the sample immediately prior to target onset. Consistent with previous results 18, the discrimination times ranged between 55-9 ms, and the phasic EMG responses to target onset persisted for about 2 ms.

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