Biomedical subjects

T S Constantinidis

Publications and source records attributed to T S Constantinidis.

5 recordsLinked to original sources

PubMed1997

Changes of presaccadic cortical activity when performing horizontal, visually guided saccades.

When a visually guided saccade task is running, the presaccadic potential obtained in the initial period of the task differs from those obtained later, while the subject's oculomotor performance remains unaffected. These time-related changes of cortical activity consist both of an overall decreasing electrical activity as well as a selective one over certain cortical areas. The generalised reduced activity already described in earlier studies is considered as an unspecified effect such as fatigue or decreased motivation. On the contrary, the pronounced selective changes of cortical activity obtained over cortical areas such as the centro-parietal and frontal cortices, should be related with more specific, that is, visuomotor function. We assume that at the beginning of the task of the performance of the saccade needs the activation of several cortical areas but later on the same oculomotor plan runs sufficiently under subcortical control.

Adult↗

PubMed1996

Cortical potentials with antisaccades.

The term antisaccade refers to saccades that are performed towards the side opposite to that of target appearance. The performance of antisaccades is considered to be determined by intact frontal inhibitory areas as patients with frontal, and especially prefrontal, lesions show a striking impairment in suppressing an unwanted protarget saccade. We recorded cortical slow potentials from subjects performing saccades and antisaccades in a task, antitask and no move conditions in order to investigate possible topographic differences between these two types of eye movement. Our main findings concern both movement related as well as sensory related potentials. With regard to the saccadic potentials, performance of an antisaccade is preceded by a much more pronounced activity during the last 100 ms prior to the eye movement onset over central-anterior leads with a slight ipsilateral lateralization. As for the sensory potentials, the target related with antisaccade performance is followed by smaller, but nonstatistically significant, exogenous responses while at 300-350 ms after target appearance, the activity associated with the antisaccade's target is clearly larger over central midline leads. Although we could not precisely relate the electrical activity obtained with well circumscribed cortical function, the results support the view that the anterior and slightly ipsilateral cortical activation which precedes the performance of an antisaccade could reflect the frontal mechanisms of suppression of the unwanted saccade.

Adult↗

PubMedDate not supplied

The increased reaction time of antisaccades. What makes the difference?

The aim of this study was the detection of the parameters involved in an already defined phenomenon, namely that the reaction time of antisaccades is greater than that of pro-target saccades. Thus, we performed four different experimental paradigms: (i) The target location was unpredictable (to the left or to the right) but the type of saccade (pro-or anti-target) was predictable. The corresponding mean values of the reaction times were 231 +/- 40 ms for anti- and 179 +/- 50 ms for pro-target saccades. (ii) Both the target position and the type of saccade were unpredictable (437 +/- 91 and 412 +/- 85 for anti-and pro-target saccades, respectively). (iii) The target location remained predictable while the type of saccade was unpredictable (397 +/- 104 and 385 +/- 90 ms) and (iv) Both the target position and the type of saccade were predictable (185 +/- 67 and 180 +/- 61). The statistical analysis (ANOVA and post hoc comparisons) revealed significant differences only in the first two experiments. Our results suggest that the antisaccades present increased latency, compared to that of pro-target saccades, only under certain experimental conditions and especially when the target location is unpredictable. We presume that the antisaccade's latency prolongation is due not to the frontal lobe inhibition but to the double interference of the parietal lobe, which has to re-reconstruct the target location in space.

Adult↗

PubMedDate not supplied

F-persistence studies in L5-S1 lumbosacral radiculopathies.

F-wave persistence of the deep peroneal nerve was studied in 41 patients with L5-S1 compressive root lesion (22 with radicular pain (RP) and 19 with motor and/or sensory (MS) signs), and in 26 normal control subjects. We used specific conditions, i.e., surface electrodes, stronger stimulus and facilitating maneuver in order to enhance the frequency of F-response appearance. EMG and nerve conduction studies were done F-latency was also measured on both sides of the patients. In the affected sides, both RP and MS, F-persistence's mean value was 56.1 and 31.0 respectively, which was significantly (p < 0.01) lower than controls (mean 83.2), and showed a significant correlation with the extensor digitorum brevis maximal interference pattern. These findings possibly reflect demyelination and/or axonal damage of lower motoneuron. Reduced F-persistence was found in 22 selected patient sides with unequivocal dorsal root damage only (mean 56.7, p < 0.01). This finding could be the result of a reduced lower motoneuron excitability because of the disruption of the circuit retaining the muscle tone. The diagnostic utility of F-persistence, F-latency and EMG was also tested. EMG and F-persistence were found statistically equal while F-persistence was found with a significant preponderance in comparison with F-latency. Finally, EMG was found more sensitive than F-latency in the patient sides with neurologic deficits.

Adult↗

PubMedDate not supplied

The effect of Jendrassik manoeuvre on the latency, amplitude and left-right asymmetry of tendon reflexes.

In order to determine the effect of the Jendrassik manoeuvre (JM) on the latency and amplitude of the electrically recorded compound action potentials of the tendon reflexes (TR) as well as on their left-right asymmetry, the above parameters of the knee (KR) and Achilles (AR) TR were measured in 52 normal subjects (32 men and 18 women) aged 18-74 years (33 +/- 12.2) both at rest and during the JM, using a commercially available tendon hammer connected with the electromyograph. The left-right difference of the latencies was not statistically significant under both conditions. The knee reflex latency--on both sides--was shortened during the JM, while that of the Achilles tendon reflex was not significantly altered. The difference of the TR amplitude between the two sides in percentage of the lower value was not significant at rest and showed a marked diminution during JM. The manoeuvre caused also a net increase of the absolute values of the compound action potentials amplitude of both reflexes.

Achilles Tendon↗