Tracking visible and occluded targets: Changes in event related potentials during motion extrapolation

Previous research suggests that there is overlap between the systems used for tracking visible and occluded moving targets. Both visually derived and stored velocity information provide input to the tracking system when the target is visible, but after occlusion the system receives its input solely from stored velocity representations. We used EEG to investigate the transition to purely memory guided tracking after the initial period of occlusion. Participants fixated while they covertly tracked targets moving horizontally rightward at velocities of 12 or 20°/s. The targets were either continuously visible or disappeared for a short interval mid trajectory. Similar positive event related components were recorded over the right occipitoparietal region in both tasks, providing further evidence that the same neural systems are involved in tracking both visible and occluded targets. Furthermore, when the target was visible, the development of this positivity was linked to the spatial location of the target, peaking earlier in the 20°/s condition. However, in the occluded condition the positive deflection began around 200 ms following the onset of occlusion and was not modulated by target velocity or location. This indicates a neural response after occlusion is cortically registered, consistent with the hypothesis that there is increased reliance on memory guided tracking at this point.     

Smooth pursuit-like eye movements during mental extrapolation of motion: the facilitatory effect of drowsiness

We studied eye movements during mental extrapolation of motion. Subjects tracked with the eyes a target oscillating sinusoidally by +/- 5 degrees on the horizontal plane at frequencies between 0.15 and 0.5 Hz. After 4 cycles the target disappeared and subjects had to mentally extrapolate its motion in imagery for 5 further cycles. Subjects were invited to relax. We recorded eye movements with infrared oculography and the lid aperture with a webcam. Typically, in the imagery phase, sequences of saccades "reproduced" the macroscopic characteristics of the to-be-imagined motion. However, slow eye movements substituting the sequence of saccades emerged repeatedly in the course of the experiment, to the extent that sometimes it was almost impossible to distinguish the pattern of eye movements during tracking from that during imagery. These smooth pursuit-like eye movements lasted up to 17 s, although they were more commonly intermingled with saccades. It turned out that this phenomenon occurred mostly, although not exclusively, when the lids were partially lowered suggesting an association with drowsiness. The average gain of smooth pursuit-like eye movements in imagery passed from 0.09 when the lids were open, to 0.27 when they were partially lowered. A control experiment excluded that the lowering of the lids per se had played any important role. This finding has implications for both the physiology of the oculomotor system and for the debate on the relation between imagery and perception.     

Action-specific extrapolation of target motion in human visual system

Neuropsychological studies have indicated two distinct visual pathways in our brain, one dedicated to conscious perception and one to visuomotor control. Some psychophysical results support this idea with normal subjects, but they are still controversial. This study provides new psychophysical evidence for the dissociation by showing action-specific extrapolation of the visual target trajectory. When a moving target disappears, the perceived final position is liable to be shifted forward (representational momentum). In experiment 1, larger and more robust forward shifts were found when the position was directly touched without seeing the screen (open-loop pointing) than when the position was judged perceptually. The most striking dissociation was that fixation did not affect the forward shift in open-loop pointing while it almost abolished the shifts in perceptual judgements. In experiment 2, this action-specific result was found to disappear after a response delay of 4000 ms. Experiments 3 and 4 confirmed that the results were not affected by the external reference frames. The specific forward shifts found in open-loop pointing suggest that the visuomotor system compensates for the neural delays by extrapolating the target motion. The results, together with earlier findings, lead to a psychophysical double dissociation of the two visual pathways.     

The volitional inhibition of anticipatory ocular pursuit using a stop signal

Unlike limb movements, smooth pursuit eye movements cannot normally be performed in the absence of a target. However, when subjects have a high expectancy of an imminent target appearance, the situation changes, and anticipatory smooth pursuit (ASP) tends to precede target onset by several hundred milliseconds. The velocity of this ASP is scaled predictively according to expected target velocity. And when an upcoming target is unexpectedly altered, or fails to appear, ASP continues regardless for approximately 150-200 ms before modification by visual feedback begins [J. Neurophysiol., 84 (2000) 2340]. These and other observations led to the earlier suggestion that ASP might be ballistic, being pre-programmed from start to finish. Two experiments with different timing parameters were therefore performed to test this hypothesis using a version of Logan's [Psychol. Rev., 91 (1984) 295] stop signal task. The aim was to test whether ASP could be stopped at will, and if so, whether the time taken to stop varied as a function of the time since ASP onset. Results showed that in response to a stop signal, ASP can be inhibited at any point in its trajectory, and for the majority of subjects in experiment 1, and all the subjects in experiment 2, with a latency that does not change significantly with target speed or time since ASP onset. These results provide the first demonstration that anticipatory movements can be stopped volitionally in response to a stop signal. Possible cognitive and neurophysiological mechanisms underlying this process are discussed.     

Delayed response to animate implied motion in human motion processing areas

Viewing static photographs of objects in motion evokes higher fMRI activation in the human medial temporal complex (MT+) than looking at similar photographs without this implied motion. As MT+ is traditionally thought to be involved in motion perception (and not in form perception), this finding suggests feedback from object-recognition areas onto MT+. To investigate this hypothesis, we recorded extracranial potentials evoked by the sight of photographs of biological agents with and without implied motion. The difference in potential between responses to pictures with and without implied motion was maximal between 260 and 400 msec after stimulus onset. Source analysis of this difference revealed one bilateral, symmetrical dipole pair in the occipital lobe. This area also showed a response to real motion, but approximately 100 msec earlier than the implied motion response. The longer latency of the implied motion response in comparison to the real motion response is consistent with a feedback projection onto MT+ following object recognition in higher-level temporal areas.     

Dynamics of anticipatory mechanisms during predictive context processing

We employed an electroencephalography paradigm manipulating predictive context to dissociate the neural dynamics of anticipatory mechanisms. Subjects either detected random targets or targets preceded by a predictive sequence of three distinct stimuli. The last stimulus in the three‐stimulus sequence (decisive stimulus) did not require any motor response but 100% predicted a subsequent target event. We showed that predictive context optimises target processing via the deployment of distinct anticipatory mechanisms at different times of the predictive sequence. Prior to the occurrence of the decisive stimulus, enhanced attentional preparation was manifested by reductions in the alpha oscillatory activities over the visual cortices, resulting in facilitation of processing of the decisive stimulus. Conversely, the subsequent 100% predictable target event did not reveal the deployment of attentional preparation in the visual cortices, but elicited enhanced motor preparation mechanisms, indexed by an increased contingent negative variation and reduced mu oscillatory activities over the motor cortices before movement onset. The present results provide evidence that anticipation operates via different attentional and motor preparation mechanisms by selectively pre‐activating task‐dependent brain areas as the predictability gradually increases.     

Don't do it! Cortical inhibition and self-attribution during action observation

Numerous studies suggest that both self-generated and observed actions of others activate overlapping neural networks, implying a shared, agent-neutral representation of self and other. Contrary to the shared representation hypothesis, we recently showed that the human motor system is not neutral with respect to the agent of an observed action [Schütz-Bosbach, S., Mancini, B., Aglioti, S. M., & Haggard, P. Self and other in the human motor system. Current Biology, 16, 1830-1834, 2006]. Observation of actions attributed to another agent facilitated the motor system, whereas observation of identical actions linked to the self did not. Here we investigate whether the absence of motor facilitation for observing one's own actions reflects a specific process of cortical inhibition associated with self-representation. We analyzed the duration of the silent period induced by transcranial magnetic stimulation of the motor cortex in active muscles as an indicator of motor inhibition. We manipulated whether an observed action was attributed to another agent, or to the subjects themselves, using a manipulation of body ownership on the basis of the rubber hand illusion. Observation of actions linked to the self led to longer silent periods than observation of a static hand, but the opposite effect occurred when observing identical actions attributed to another agent. This finding suggests a specific inhibition of the motor system associated with self-representation. Cortical suppression for actions linked to the self might prevent inappropriate perseveration within the motor system.     

The development of anticipatory action planning in children with unilateral cerebral palsy

Background Previous studies suggest that compromised bimanual performance experienced by children with unilateral cerebral palsy (CP) is not only due to difficulties in action execution but may also be a result of impaired anticipatory action planning.Aims The effect of age and side of hemiplegia were examined and the relationship between anticipatory action planning, unimanual capacity and bimanual performance was explored.Methods and procedures Using a multi-centre, prospective, cross-sectional observational design, anticipatory action planning was analyzed in 104 children with unilateral cerebral palsy, aged 6–12 years, using the sword task.Outcomes and results Anticipatory action planning did not improve with age in children with unilateral CP, aged between 6–12 years. No differences were found between children with left or right hemiplegia. Finally, anticipatory action planning was not related to unimanual capacity or bimanual performance.Conclusion and implications This study demonstrates anticipatory action planning, measured using the sword task, does not improve with age in children with unilateral CP and is not related to bimanual performance or laterality. Future studies of anticipatory action planning in children with unilateral CP should consider using measures that require effective anticipatory action planning for successful task completion rather than end state comfort.     

Delayed onset of inhibition of return in schizophrenia

Peripheral visual cues occuring before a subsequent target result in an almost immediate facilitatory and then a later inhibitory effect on target detection. In a detailed parametric investigation, the authors compared schizophrenic subjects (SCZ) and control subjects (CONT) to examine whether they showed any differences in the time course of these nonpredictive peripheral cuing effects. Subjects fixated a central position and made saccadic responses to visual targets. Targets were presented 10 degrees to the left or right of fixation and were preceded at various time intervals by visual cues. Targets occurred with equal probability in either the same position as the cue or in the opposite, uncued location, and 10 delay periods were used corresponding to stimulus onset asynchronies (SOAs) of 66, 79, 106, 133, 159, 226, 305, 505, 705, and 1000 ms. All subjects showed facilitation for short cue-target delays and inhibition of return (IOR) for longer delays. SCZ, however, showed an apparent shift in the time course of cuing effects in the form of a delayed onset of IOR. Using a task of reflexive orienting, these results support findings of a delayed rather than an absent inhibitory process in medicated SCZ.     

The influence of trait anxiety on autonomic response and cognitive performance during an anticipatory anxiety task

The interaction between emotion and cognition is thought to be intimately involved in the development and maintenance of anxiety disorders. In a set of studies, we investigated whether trait anxiety modulates cognitive performance and autonomic activity during an anticipatory anxiety task. Participants completed a letter-size decision-making task with two alternating 28-32 s background screen color-blocks. One of the colors was associated with the presentation of an aversive noise [unconditioned stimulus (UCS)]. Participants were aware of the background color that would (CTX+) and would not (CTX-) be paired with the UCS but did not know when or how often the UCS would be presented. Two experiments were conducted. In Experiment 1, the UCS was presented during the decision-making task in the CTX+ color-blocks using a partial reinforcement schedule. Different noises were presented each time to increase unpredictability and prevent habituation. In Experiment 2, the UCS was never presented during the decision-making task. Results suggested that only the paradigm used in Experiment 1 was successful in eliciting anticipatory anxiety. In Experiment 1, continuously measured skin conductance response (SCR) data suggested that anxiety was significantly greater during CTX+ compared to CTX- trials; no SCR differences were found between high and low trait-anxious participants. Results further indicated that high trait-anxious participants responded significantly faster on the decision-making task during CTX+ compared to CTX- trials, whereas low trait-anxious participants displayed the opposite pattern. Our results reveal an interesting dissociation between the effects of individual differences in trait anxiety on autonomic activity and cognitive performance during an anticipatory anxiety task.     

Brain activation during anticipatory anxiety in social anxiety disorder

Exaggerated anticipatory anxiety during expectation of performance-related situations is an important feature of the psychopathology of social anxiety disorder (SAD). The neural basis of anticipatory anxiety in SAD has not been investigated in controlled studies. The current study used functional magnetic resonance imaging (fMRI) to investigate the neural correlates during the anticipation of public and evaluated speaking vs a control condition in 17 SAD patients and 17 healthy control subjects. FMRI results show increased activation of the insula and decreased activation of the ventral striatum in SAD patients, compared to control subjects during anticipation of a speech vs the control condition. In addition, an activation of the amygdala in SAD patients during the first half of the anticipation phase in the speech condition was observed. Finally, the amount of anticipatory anxiety of SAD patients was negatively correlated to the activation of the ventral striatum. This suggests an association between incentive function, motivation and anticipatory anxiety when SAD patients expect a performance situation.     

Transient and sustained brain activity during anticipatory visuospatial attention

In this study, we determined whether the visuospatial attention network of frontal, parietal, and occipital cortex can be parsed into two different subsets of active regions associated with transient and sustained processes within the same cue-to-target delay period of an endogenously cued visuospatial attention task. We identified regions with early transient activity and regions with later sustained activity during the same trials using a general linear model analysis of event-related BOLD functional MRI data with two timecourse covariates for the same cue-to-target delay period. During the delay between the cue and target, we observed significant transient activity in right frontal eye field and right occipital-parietal junction, and significant sustained activity in right ventral intraparietal sulcus and right dorsolateral and anterior prefrontal cortex.     

Event-related desynchronization during anticipatory attention for an upcoming stimulus: a comparative EEG/MEG study.

OBJECTIVES: Our neurophysiological model of anticipatory behaviour (e.g. Acta Psychol 101 (1999) 213; Bastiaansen et al., 1999a) predicts an activation of (primary) sensory cortex during anticipatory attention for an upcoming stimulus. In this paper we attempt to demonstrate this by means of event-related desynchronization (ERD). METHODS: Five subjects performed a time estimation task, and were informed about the quality of their time estimation by either visual or auditory stimuli providing Knowledge of Results (KR). EEG and MEG were recorded in separate sessions, and ERD was computed in the 8-10 and 10-12 Hz frequency bands for both datasets. RESULTS: Both in the EEG and the MEG we found an occipitally maximal ERD preceding the visual KR for all subjects. Preceding the auditory KR, no ERD was present in the EEG, whereas in the MEG we found an ERD over the temporal cortex in two of the 5 subjects. These subjects were also found to have higher levels of absolute power over temporal recording sites in the MEG than the other subjects, which we consider to be an indication of the presence of a 'tau' rhythm (e.g. Neurosci Lett 222 (1997) 111). CONCLUSIONS: It is concluded that the results are in line with the predictions of our neurophysiological model.     

Knee trembling during freezing of gait represents multiple anticipatory postural adjustments

Freezing of gait (FoG) is an episodic, brief inability to step that delays gait initiation or interrupts ongoing gait. FoG is often associated with an alternating shaking of the knees, clinically referred to as knee trembling or trembling in place. The pathophysiology of FoG and of the concomitant trembling knees is unknown; impaired postural adjustment in preparation for stepping is one hypothesis. We examined anticipatory postural adjustments (APAs) prior to protective steps induced by a forward loss of balance in 10 Parkinson's disease (PD) subjects with marked FoG and in 10 control subjects. The amplitude and timing of the APAs were determined from changes in the vertical ground-reaction forces recorded by a force plate under each foot and were confirmed by electromyographic recordings of bilateral medial gastrocnemius, tibialis anterior and tensor fascia latae muscles. Protective steps were accomplished with a single APA followed by a step for control subjects, whereas PD subjects frequently exhibited multiple, alternating APAs coexistent with the knee trembling commonly observed during FoG as well as delayed, inadequate or no stepping. These multiple APAs were not delayed in onset and were of similar or larger amplitude than the single APAs exhibited by the control subjects. These observations suggest that multiple APAs produce the knee trembling commonly associated with FoG and that FoG associated with a forward loss of balance is caused by an inability to couple a normal APA to the stepping motor pattern.     

Processing of irrelevant visual motion during performance of an auditory attention task

The extent to which irrelevant perception of visual motion distractors can be modulated by manipulating auditory load in a relevant task was assessed with Positron Emission Tomography (PET) and behavioural experiments. Subjects performed an auditory task and ignored an irrelevant visual motion stimulus, under two conditions. In a low load condition, subjects were asked to detect words spoken in a loud voice among words spoken in a quiet voice, while in a high load condition they attempted to detect bisyllabic words among monosyllabic and trisyllabic words. We found that motion-related visual areas were strongly activated by the irrelevant motion stimulus, compared to a static stimulus, under both conditions of load in the auditory task. In a second behavioural experiment, the duration of the motion after-effect was similarly unaffected by adaptation under low or high auditory load. These results are in clear contrast with the strong modulation of irrelevant motion processing by visual load, as reflected in the duration of the motion after effect (Section 6) and neural responses in motion-related visual areas (Rees et al., Science, (1997) 278, 338). These findings support the claim that attentional capacity is restricted within but not between sensory modalities, and indicate that processing of visual distractors may occur whenever there is sufficient visual capacity to process them, despite being task- and modality-irrelevant.     

Delayed inhibition creates amplitude tuning of mouse inferior collicular neurons

Nonmonotonic intensity response neurons referred as amplitude-tuned neurons are considered to be created by high-threshold inhibition in auditory system. Very limited information, however, is available on how the inhibition works for amplitude-tuned neurons. We studied the temporal response properties of these neurons with or without iontophoresis of bicuculline (gamma-aminobutyric acid A antagonist). In most neurons, the firing durations gradually reduced with the increasing amplitudes beyond the best amplitudes. Bicuculline application selectively blocked the inhibition of the sustained responses to high amplitudes and abolished the nonmonotonic intensity response properties. Our results suggest that a temporally delayed inhibition, whose latency reduced related to excitation with the increasing amplitude, is responsible for the creation of about 71% amplitude-tuned neurons in mouse inferior colliculus.     

Henri Laborit and the inhibition of action

Henri Laborit was one of the founders of modern neuropsychopharmacology, having discovered, or participated in, the discovery of chlorpromazine, gamma-OH, clomethiazole, and minaprine. He also put forward a theory regarding the necessity of counteracting the negative consequences of defense mechanisms during anesthesia or behavioral inhibition. The scope of his work covers neurophysiology, pharmacology, psychiatry, and psychosomatics. His independence of spirit meant that most of his research was not done within university settings.     

Specific activation of histaminergic neurons during daily feeding anticipatory behavior in rats

When food is available during a restricted and predictable time of the day, animals show increased locomotor and food searching behaviors before the anticipated daily meal. We had shown that histamine-containing neurons are the only aminergic neurons related to arousal that become active in anticipation of an upcoming meal. To further map, the brain regions involved in the expression of the feeding-anticipatory behavior, we quantified the expression of Fos in hypothalamic areas involved in arousal. We found that nearly 35% of the histamine neurons from the tuberomammillary nucleus were Fos-immunoreactive immediately before mealtime. One hour before this transient increase in Fos-immunoreactivity, we found a similarly brief increase of fos mRNA in the tuberomammillary nucleus. In contrast, the activation of two types of perifornical hypothalamic neurons followed meal onset by 1-2 h. One neuron type was orexin/hypocretin-immunoreactive, while the other type was neither orexin nor melanin concentrating hormone-immunoreactive. The present work indicates that the increased locomotor activity that anticipates mealtime coincides with the activation of the tuberomammillary nucleus, and that the behavioral activation during the consummatory phase of feeding coincides more closely with the delayed activation of the perifornical hypothalamic area.