Motor imagery and visual event recognition.

In order to investigate the influence of covert motor processes in the recognition of visual events, we compared the response times (RT) in two similar tasks, one involving a to-be-grasped object and the other involving a to-be-observed object. In one task, we asked right-handed subjects to tell whether an observed screwdriver presented in different orientations and rotating on its main axis was screwing or unscrewing (screwdriver task). In the other task the visual stimuli were precisely the same, but subjects had to think of the screwdriver as being the pivot pin of an imagined clock, turning its hands from the back (clock task). They had to tell whether the imagined clock hands were moving clockwise or counterclockwise. In the screwdriver task, a prominent right-left asymmetry consisting of higher RTs for stimulus orientations awkward for a right-hand grip was present, suggesting that subjects adopted a strategy based upon mentally simulating the grabbing of the screwdriver handle with the dominant hand. Consistent with the hypothesis that the crucial factor that triggers these motor imagery processes is the "graspability" of the relevant object in the scene, in the clock task the right-left asymmetry disappeared in most subjects, RTs mirroring the symmetry of the visual stimuli. These findings indicate that, when interpreting a scene involving a to-be-grasped object, a strategy based upon motor imagery (mental grasping), probably unfolding procedural knowledge, is activated. When the scene involves a to-be-observed object, the recognition task can be accomplished through other, possibly visual, strategies.

Saccades to mentally rotated targets.

In order to investigate the role of mental rotation in the directional control of eye movements, we instructed subjects to make saccades in directions different from that of a visual stimulus (rotated saccades). Saccadic latency increased linearly with the amount of directional transformation imposed between the stimulus and the response. This supports the hypothesis that reorienting a saccade is accomplished through a mental rotation process. No differences were found in amplitude, duration, velocity, and curvature between rotated and visually guided saccades. Analogous to mental rotation tasks involving reaching arm movements, it is surmised that frontal/prefrontal cortical structures participate in rotated saccades by reorienting the intended saccadic direction. A linear increase in response time with the imposed directional transformation was also found in an analogous mental task not requiring a directed motor response, namely, mentally localizing a point in space at a certain angle from a stimulus direction. However, the speed of mental rotation was systematically lower than in the rotated saccade task. These findings indicate that mental rotation is a rather general mechanism through which directional transformations are achieved.

Recognizing the motion of a graspable object is guided by handedness.

Subjects viewing a rotating screwdriver presented in a motion picture were asked whether it was screwing or unscrewing. A difference emerged in the performance of right- and left-handers. In right-handers, stimulus orientations particularly awkward for a right-hand grip determined higher response times, compared with visually equivalent but more comfortable orientations. When they were also requested to imagine their right hand grasping the screwdriver, similar results were obtained. By imagining the left hand, response times increased and the differences between awkward and comfortable orientations disappeared. In contrast, consistent with their manual dominance, left-handers response times were similar to those obtained when imagining the left but distinct from those obtained when imagining the right hand. We conclude that handedness may guide the interpretation of visual events involving manipulable objects.

The early phase of horizontal optokinetic responses in the pigmented rat and the effects of lesions of the visual cortex.

Horizontal optokinetic responses of pigmented rats were studied both in intact animals and in animals that had received lesions of the visual area of the cerebral cortex. In response to uniform velocity stimulation, there was an initial phase of rapid acceleration, larger than that reported in earlier studies, followed by a period of fairly uniform acceleration until the eye velocity approached that of the stimulus. As reported previously, responses to monocular stimulation were highly asymmetric, with the responses to nasotemporal stimulation being much weaker than those to temporonasal stimulation. Responses to sinusoidal stimulation were also studied. No significant effect of cortical lesions on the responses was seen.

The relationship between curvature and velocity in two-dimensional smooth pursuit eye movements.

Curvature and tangential velocity of voluntary hand movements are constrained by an empirical relation known as the Two-Thirds Power Law. It has been argued that the law reflects the working of central control mechanisms, but it is not known whether these mechanisms are specific to the hand or shared also by other types of movement. Three experiments tested whether the power law applies to the smooth pursuit movements of the eye, which are controlled by distinct neural motor structures and a peculiar set of muscles. The first experiment showed that smooth pursuit of elliptic targets with various curvature-velocity relationships was most accurate when targets were compatible with the Two-Thirds Power Law. Tracking errors in all other cases reflected the fact that, irrespective of target kinematics, eye movements tended to comply with the law. Using only compatible targets, the second experiment demonstrated that kinematics per se cannot account for the pattern of pursuit errors. The third experiment showed that two-dimensional performance cannot be fully predicted on the basis of the performance observed when the horizontal and vertical components of the targets used in the first condition were tracked separately. We conclude that the Two-Thirds Power Law, in its various manifestations, reflects neural mechanisms common to otherwise distinct control modules.

Influence of eye motion on adaptive modifications of the vestibulo-ocular reflex in the rat.

While sustained retinal slip is assumed to be the basic conditioning stimulus in adaptive modifications of the vestibulo-ocular reflex (VOR) gain, several observations suggest that eye motion-related signals might also be involved. We oscillated pigmented rats over periods of 20 min around the vertical axis, at 0.3 Hz and 20 degrees/s peak velocity, in different retinal slip and/or eye motion conditions in order to modify their VOR gain. The positions of both eyes were recorded by means of a phase-detection coil system with the head restrained. The main findings came from the comparison of two basic conditions--including their respective controls--in which one or both eyes were reversibly immobilised by threads sutured to the eyes. In the first condition the animals were rotated in the light with one eye immobilised and the other eye free to move but covered. Rotation in the light in this open-loop condition immediately elicited high-gain compensatory eye movements of the non-impeded, covered eye. At the end of this training procedure, the VOR gain increased by 43.2%. In the second condition, both eyes were immobilised and one eye was covered. The result was an increase in the VOR gain of 26.3%. These two conditions were similar as to the visuo-vestibular drive during the exposure, but different as to the resulting--and allowed--eye motion, showing that the condition where the larger eye movements occurred yielded the larger VOR gain change. Our data support the idea proposed by Collewijn and Grootendorst (1979, p. 779) and Collewijn (1981, p. 146) that "[retinal] slip and eye movements seem to be relevant signals for the adaptation of the rabbit's visuo-vestibular oculomotor reflexes".(ABSTRACT TRUNCATED AT 250 WORDS)

Visual tuning to kinematics of biological motion: the role of eye movements.

The visual system is particularly sensitive to the covariation between velocity and curvature that constraint biological motion. Previous work showed that, when this biological constraint is satisfied, simple elliptical motion of a dot looks constant, although its velocity is highly non-uniform. This paper addresses the hypothesis that such a dynamic illusion is dependent upon smooth pursuit eye movements. Subjects had to adjust the kinematics of a dot moving along elliptical trajectories until they perceived a constant velocity. Different pursuit and fixation conditions were tested. The research shows that the dynamic illusion is largely independent of eye movements, suggesting that the visual system has access to implicit knowledge of motor constraints regardless of the concurrent oculomotor commands.

Vergence compensation during binocularly- and monocularly-evoked horizontal optokinetic nystagmus in the pigmented rat.

During horizontal optokinetic nystagmus evoked by binocular stimulation in the rat, the slow phases are well-conjugate. The fast phases in the adducting eye are on average about 2 deg greater in amplitude than those of the abducting eye. This causes a transient convergence which is compensated for by a divergent drift within the 100 msec following the fast phase. The amplitudes of these convergence-divergence components fluctuates somewhat from one fast phase to another and their relative amplitudes may differ. As a consequence differences in vergence between successive slow phases may occur. Such differences are usually of small amplitude, but may be as large as 5 deg. When optokinetic nystagmus is evoked by monocular stimulation, the slow phase velocities are different in the two eyes, giving a disjunctive component which is compensated for by a difference in the relative amplitudes and velocities of the fast phases in the two eyes. However, the divergent drift immediately following the fast phases is very similar whatever form of stimulation is employed. It is suggested that during monocularly-evoked optokinetic nystagmus the oculomotor system compensates for the disjunctive component arising during the slow phases by giving a different balance to the pulses of innervation of two eyes, resulting in fast phases of different amplitude.

Effects of inferior olive inactivation and lesion on the activity of medial vestibular neurons in the rat.

In anaesthetized rats, the unitary activity from the medial vestibular nucleus had been recorded during horizontal sinusoidal rotation in the absence of visual stimulation. In the first series of experiments, the inferior olivary nuclei were selectively destroyed by means of 3-acetylpyridine. Unitary activity was recorded three to five days or one month after the lesion. A few days after the lesion, the average spontaneous activity, as well as the peak-to-peak amplitude of the modulation of the medial vestibular neurons during sinusoidal rotation, were significantly lower compared to those recorded in intact rats, and to those recorded one month after the lesion. In the second series of experiments, during reversible cooling of the inferior olive region of one side, in the contralateral medial vestibular nuclei 57% of units underwent a clear decrease in firing rate accompanied by a decrease in the amplitude of modulation. In rats whose inferior olivary nuclei had been destroyed by means of 3-acetylpyridine one month before, or whose cerebellum had been removed, there were few units that showed a decrease of the firing rate and modulation amplitude on cooling the same olivary region. Our experiments show that silencing the activity of the inferior olive causes a decrease both in the spontaneous firing rate and in the amplitude of the response of the vestibular neurons to natural labyrinthine stimulation. These results support the hypothesis that the inferior olive, by changing its firing rate, may regulate on-line the gain of reflexes which are under cerebellar control.

[New aspects concerning the corpus luteum]. / Nuovi aspetti riguardanti il corpo luteo.

We have summed up current knowledge about the formation and lysis of corpus luteum with the co-ordinate intervention of luteotrophic and luteolytic factors. Then we re-examined the function of the corpus luteum in the physiologic menstrual cycle and in the first period of pregnancy, with special attention to luteal insufficiency as a cause of endocrine miscarriage.

[Antibiotic prophylaxis in obstetric surgery. Experience with a sulbactam-ampicillin combination]. / Profilassi antibiotica in chirurgia ostetrica. Esperienza con l'associazione sulbactam-ampicillina.

Antibiotic prophylaxis reduces the incidence of infections after some types of surgical interventions; in Obstetrics it can prevent infections in high risk situations. Infections can occur in particular situations, even in cesarean sections (CS) at low risk. The incidence of puerperal endometritis is variable in literature, while the incidence of pelvic or surgical wound infections is 3.8% in elective CS with respect to 7.5% in emergency CS. This study verifies the efficacy of the sulbactam-ampicillin association (Unasyn, Pfizer) in the prophylaxis of all cesarean sections, complicated or not. Unasyn was administrated one hour prior to CS and 8 and 16 hours after CS in 162 patients. Therapy was continued in 8 cases because of high risk for infection. The evaluation of the efficacy of the drug was based on clinical criteria. There were no complications or fever recorded and no toxic or allergic reactions occurred. Antibiotic prophylaxis is recommended for all patients undergoing CS.

Long-term habituation of the acoustic startle response: role of the cerebellar vermis.

The cerebellar vermis has been recognized as a key region of a circuit essential for long-term habituation of the acoustic startle response in rats. The removal of this neuronal structure before training prevents the build-up of this long-term behavioral change. Our data show that, when the same lesion is performed after training for long-term habituation, the learned behavior is not affected. These results indicate that the cerebellar vermis is essential for the acquisition, but not for the retention of long-term habituation of the startle response.

Magnesium deficiency affects the pentylenetetrazol-induced convulsions in magnesium-deprived rats.

A group of 11 young albino rats was fed with a Mg2+ free diet. After a few days, the animals showed typical signs of Mg2+ deficiency, consisting in skin vasodilation, red conjunctiva and hair loss. Pentylenetetrazol (50 mg/kg i.p.) injected in these rats, 6 and 12 days after the beginning of the diet, elicited a more severe convulsive activity compared with that shown by a control group of 12 rats. These results suggest that a Mg2+ deficiency, though not necessarily responsible for the convulsive activity, may contribute to facilitate an epileptic episode or may lead to more severe convulsions. The possibility of a more powerful activation of the NMDA receptors in Mg2+ deficiency is discussed.

Lesions of the inferior olive do not affect long- or short-term habituation of the acoustic startle response in rats.

Short- and long-term habituation of the acoustic startle response were assessed in a group of inferior olive-lesioned rats. Neither short- and long-term habituation, nor the performance of the reflex, were affected by the lesion. Since the cerebellar vermis is essential for long-term habituation of this reflex, we suggest that climbing fibres are not involved in this form of learning, which would therefore be mediated by the other cerebellar input, presumably the mossy fibres.