Inferring the future target trajectory from visual context: is visual background structure used for anticipatory smooth pursuit?

Anticipatory pursuit is not exclusively based on the recent history of target motion ("temporal anticipation"): it can also use static visual cues ("non-temporal anticipation"). Large non-temporal anticipatory changes of the direction of smooth pursuit are observed when the future trajectory of the target can be inferred from a visual "path cue" (Ladda et al. Exp Brain Res 182:343-356, 2007). It is not known whether these anticipatory responses can be considered an example of volitional pursuit or whether a more automatic, fast mechanism exists that associates the visual shape of the path cue with a future change of target motion. We therefore compared anticipatory direction changes induced by path cues with those induced by more symbolic visual cues. Further, we measured the processing time of path cues by keeping them ambiguous until 300 ms before the target entered the curve. The cues became unambiguous either when a missing part of the path cue suddenly appeared or when a misleading (invalid) path cue disappeared. Five main results suggest that the non-temporal smooth pursuit anticipation induced by path cues is due to a particular visual processing of the cue, rather than to a general volitional smooth pursuit component: (1) A curved static band providing detailed spatial information about the target's trajectory was much more efficient than more symbolic visual cues. (2) The latency for processing the path cue was less than 200 ms. (3) The effect of the path cue did not depend on a visual transient in the retinal periphery. (4) It critically depended on the spatial relation between path cue and target trajectory. (5) The anticipatory response decreased, but was still highly significant when the path cue was non-informative with respect to the future target trajectory. These findings indicate that anticipatory modifications of ongoing pursuit do not rely exclusively on the processing of motion signals, but can directly interact with low-level processes analyzing background structures.

Parkinsonian patients show impaired predictive smooth pursuit.

To determine if patients with Parkinson's disease (PD) are able to use a visual contextual cue to induce a predictive change in smooth pursuit direction and if this ability depends on the state of the dopaminergic system, we measured predictive smooth pursuit in nine patients with mild to moderate PD during OFF and ON medication. These values were compared with those of nine age-matched and sex-matched healthy controls.Our focus was on the horizontal smooth pursuit when subjects pursued a downward moving target entering a+/-90 deg curve. The target moved on a homogeneous background or on a static "street" that indicated the future trajectory of the target. Our main result is that PD patients were impaired in eliciting predictive smooth pursuit using the context information of the street compared to healthy subjects. The control group elicited predictive pursuit 250 ms before target onset. In contrast, PD patients showed significantly longer latency (100-120 ms) and reduced maximal pursuit velocity. However, without the street guiding pursuit, a delay of about 250 ms was seen in both groups. There was no significant difference in the smooth pursuit performance between OFF and ON medication in the patient group.These results show that early stage PD patients are impaired in the use of static visual information as a cue for predictive pursuit compared to controls and that this deficit does not depend on dopaminergic medication. In the context of predictive eye movement, the involvement of the striatal-frontal pathway and the spatial working memory is discussed.

Quantitative sensory testing in cluster headache: increased sensory thresholds.

To determine if recently reported changes in sensory thresholds during migraine attacks can also be seen in cluster headache (CH), we performed quantitative sensory testing (QST) in 10 healthy subjects and in 16 patients with CH. Eight of the patients had an episodic CH and the other eight a chronic CH. The tests were performed on the right and left cheeks and on the right and left side of the back of the hands to determine the subjects' perception and pain thresholds for thermal (use of a thermode) and mechanical (vibration, pressure pain thresholds, pin prick, von Frey hairs) stimuli. Six patients were examined in the attack-free period. Three were also willing to repeat the tests a second time during an acute headache attack, which was elicited with nitroglycerin. The healthy subjects performed the experiments in the morning and evening of the same day to determine if sensory thresholds are independent of the time of day. If they were, this would allow estimation of the influence of the endogenous cortisone concentration on these thresholds. The control group showed no influence of the time of day on the thresholds. There was a significant difference in pain sensitivity between the back of the hands and the cheeks (P<0.05): higher thresholds were found on the back of the hands. The thresholds generally exhibited little intersubject variability, indicating that QST is a reliable method. There was also a significant difference between the test areas in the patient group (P<0.001): the cheeks were also more sensitive than the back of the hands. In comparison with reference data of healthy volunteers, the detection thresholds were increased in the patients on both test areas. These were statistically significant for warmth, thermal sensory limen (TSL), heat and pressure on the back of the hands (P<0.04) and for the warmth and TSL thresholds on the cheeks (P<0.05). There were no differences in the thresholds regardless of whether the patients were examined in or outside of a cluster bout. Furthermore, we found no cutaneous allodynia in the three patients tested during an attack. The increased sensory thresholds on the cheeks as well as on the back of the hands are in agreement with an increased activation of the patients' antinociceptive system. The seasonal variation and the temporal regularity of single attacks as well as the findings in imaging studies indicate that the hypothalamus is involved in the pathophysiology of CH. In view of the strong connectivity between the hypothalamus and areas involved in the antinociceptive system in the brainstem, we hypothesize that this connection is the reason for the increased sensory thresholds in CH patients found in our study.