Smooth pursuit pathways

Cerebral pathways subserving smooth pursuit. Adapted from a slide by R. John Leigh (personal communication) by Michael MacAskill and Tim Anderson

Clinical features of all patients.

*<p>On clinical examination, most patients and age-matched controlled subjects showed mild limitation of upgaze and mild impairment of convergence and smooth pursuit. HYS: Hoehn-Yahr Scale for Parkinsons’ disease <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058535#pone.0058535-Hoehn1" target="_blank">[18]</a> **All PSP patients showed impaired smooth pursuit and vergence eye movements.</p

Examples of saccadic intrusions in a control subject, a PSP patient, a PD patient, a CBS patient, a MSA patient and a SCASI patient.

<p>SWJs were present in all subject groups, although they were smaller and less frequent in healthy controls. Each trace represents a 5 s recording of horizontal eye positions containing SWJs. Horizontal position and timescales for all traces are as in the bottom trace.</p

Characteristics of fixational saccades across subject groups.

<p>First row, saccadic peak velocity/magnitude relationships. Second row, saccadic duration/magnitude relationships. Third row, saccade magnitude distributions. Fourth row, polar histograms of saccade directions. Each graph shows the combined data for all subjects in each group.</p

Saccadic parameters in PD patients, PSP patients and healthy controls.

<p>Saccade rates, magnitudes, peak velocity-magnitude relationship slopes and vertical components (of saccade direction) are indicated. Bars represent the average value across subjects of each group and the error bars indicate the standard error of the mean. Asterisks show significance (p<0.05, t-test).</p

Saccadic parameters in PD patients, PSP patients and healthy controls.

<p>Bold text indicates statistical significance.</p

Microsaccade triggering model [<b>14</b>].

<p>SC neurons present two gradients of connectivity, one that is strongest between rostral SC and OPNs, and one that is strongest between caudal SC and EBNs and IBNs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058535#pone.0058535-Gandhi1" target="_blank">[59]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058535#pone.0058535-BttnerEnnever1" target="_blank">[61]</a> (longer lines represent stronger connections). The mutually inhibited OPNs and IBNs act as a trigger. During fixation, rostral SC activity drives the OPNs that inhibit the EBNs and IBNs. Directly preceding the launch of a microsaccade, activity in the rostral area shifts slightly caudally. At some point the balance of inhibition is broken, and the IBNs inhibit the OPNs more than the OPNs inhibit the IBNs. Then the EBNs start to burst initiating the microsaccade. Note that this representation is a one-dimension simplification of the circuit. The circuit functions in the same manner for vertical (up and down) BNs. Minus signs indicate inhibitory connections, plus signs excitatory ones.</p

Summary of the stability of gaze in 20 healthy control subjects as they fixed upon a small visual target with one eye while their other eye was covered.

<p>Panel A shows the distribution of measurements of standard deviation (SD) of eye position; the percentile values on these box plots, and in subsequent figures, are indicated (50% is the median). Panel B summarizes median speed of eye drifts during monocular fixation. For the group of subjects, there was no significant difference in the SD of eye position or median speed between the viewing and covered eyes.</p

Summary of measurements of ratio of peak velocity of bad eye/peak velocity of good eye for upward and downward saccades of the group of control subjects (CS) and P1-4, who had monocular loss of vision early in life.

<p>Box plot conventions are similar to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056556#pone-0056556-g001" target="_blank">Figure 1</a>. Perfectly conjugate saccades would have a ratio of 1.0. Upward saccades made by the patients are generally more conjugate than downward saccades.</p

Summary of measurements of gaze stability, expressed as median eye speed, for 20 control subjects (box plots) and for individual patients studied for each directional component.

<p>For patients with monocular visual loss, SD values of eye speed were greater in the eyes with poorer vision (less so for P5 and P6 with late onset of visual loss due to ARMD). The fastest eye-drift speeds were shown by P7, who had been blind since birth.</p