Random Interstimulus Intervals Research Articles

ERP evidence of attentional somatosensory processing and stimulus-response coupling under different hand and arm postures.

We investigated (1) the effects of divided and focused attention on event-related brain potentials (ERPs) elicited by somatosensory stimulation under different response modes, (2) the effects of hand position (closely-placed vs. separated hands) and arm posture (crossed vs. uncrossed forearms) on the attentional modulation of somatosensory ERPs, and (3) changes in the coupling of stimulus- and response-related processes by somatosensory attention using a single-trial analysis of P300 latency and reaction times. Electrocutaneous stimulation was presented randomly to the thumb or middle finger of the left or right hand at random interstimulus intervals (700-900 ms). Subjects attended unilaterally or bilaterally to stimuli in order to detect target stimuli by a motor response or counting. The effects of unilaterally-focused attention were also tested under different hand and arm positions. The amplitude of N140 in the divided attention condition was intermediate between unilaterally attended and unattended stimuli in the unilaterally-focused attention condition in both the mental counting and motor response tasks. Attended infrequent (target) stimuli elicited greater P300 in the unilaterally attention condition than in the divided attention condition. P300 latency was longer in the divided attention condition than in the unilaterally-focused attention condition in the motor response task, but remained unchanged in the counting task. Closely locating the hands had no impact, whereas crossing the forearms decreased the attentional enhancement in N140 amplitude. In contrast, these two manipulations uniformly decreased P300 amplitude and increased P300 latency. The correlation between single-trial P300 latency and RT was decreased by crossed forearms, but not by divided attention or closely-placed hands. Therefore, the present results indicate that focused and divided attention differently affected middle latency and late processing, and that hand position and arm posture also differently affected attentional processes and stimulus-response coupling.

O031 The Inter-stimulus Interval Effect in the Psychomotor Vigilance Task

Abstract Introduction The Psychomotor Vigilance Task (PVT) is a widely used measure of the effects of sleep deprivation on vigilant attention. The test requires a rapid response to a stimulus occurring at random inter-stimulus intervals (ISIs) between 2 and 10 seconds following a previous response. A few studies have found an ISI effect where shorter ISIs (2-4s) have slower reaction times (RTs) than longer ISIs (8-10s). How this ISI effect is impacted by circadian timing has yet to be investigated. Method This study compared the ISI effect at 3 time points coinciding with 5, 23 (circadian trough), and 29 hours of wakefulness. Data were taken from 16 healthy participants during a 30 hour period of sleep deprivation. Results A repeated-measures (3 x 3) ANOVA (3 time points, 3 ISIs) found that RTs were slower and lapses (RT>500msec) more frequent in short ISIs compared with medium and long ISIs. RTs were also slower and lapses more frequent at the circadian trough compared to both the early testing session and after 29h of total sleep deprivation. Discussion Increased lapses in shorter ISIs could be explained by an involuntary mental “rest period” after responding, that gets longer and more frequent under sleep pressure from both circadian and homeostatic sleep pressure. These findings have implications for interpreting PVT results and their application to everyday tasks, such as driving. Further research could involve neuroimaging the brain’s responses during different ISIs to confirm the mental ‘rest period’ following a response in the PVT task.

Vibration Alert to the Brain: Evoked and Induced MEG Responses to High-Frequency Vibrotactile Stimuli on the Index Finger of Dominant and Non-dominant Hand.

Background: In recent years, vibrotactile haptic feedback technology has been widely used for user interfaces in the mobile devices. Although functional neuroimaging studies have investigated human brain responses to different types of tactile inputs, the neural mechanisms underlying high-frequency vibrotactile perception are still relatively unknown. Our aim was to investigate neuromagnetic brain responses to high-frequency vibrotactile stimulation, using magnetoencephalography (MEG).Methods: We measured 152-channel whole-head MEG in 30 healthy, right-handed volunteers (aged 20–28 years, 15 females). A total of 300 vibrotactile stimuli were presented at the tip of either the left index finger or the right index finger in two separate sessions. Sinusoidal vibrations at 150 Hz for 200 ms were generated with random inter-stimulus intervals between 1.6 and 2.4 s. Both time-locked analysis and time-frequency analysis were performed to identify peak responses and oscillatory modulations elicited by high-frequency vibrations. The significance of the evoked and induced responses for dominant and non-dominant hand stimulation conditions was statistically tested, respectively. The difference in responses between stimulation conditions was also statistically evaluated.Results: Prominent peak responses were observed at 56 ms (M50) and at 100 ms (M100) for both stimulation conditions. The M50 response revealed clear dipolar field patterns in the contralateral side with significant cortical activations in the contralateral primary sensorimotor area, whereas the M100 response was not as prominent as the M50. Vibrotactile stimulation induced significant suppression of both alpha (8–12 Hz) and beta (20–30 Hz) band activity during the mid-latency period (0.2–0.4 s), primarily in sensorimotor areas contralateral to the stimulation side. In addition, a significant alpha enhancement effect in posterior regions was accompanied with alpha suppressions in sensorimotor regions. The alpha suppression was observed in a broader distribution of cortical areas for the non-dominant hand stimulation.Conclusion: Our data demonstrate that high-frequency tactile vibrations, which is known to primarily activate Pacinian corpuscles, elicit somatosensory M50 and M100 responses in the evoked fields and induce modulations of alpha and beta band oscillations during mid-latency periods. Our study is also consistent with that the primary sensorimotor area is significantly involved in the processing of high-frequency vibrotactile information with contralateral dominance.

Proposal of conditional random inter-stimulus interval method for unconstrained enclosure based GPIAS measurement systems.

Gap prepulse inhibition of acoustic startle (GPIAS) method has been used effectively for the objective assessment of tinnitus in animals. Among two types of enclosures for the GPIAS, the unconstrained type carries less risk of animal death due to the absence of binding stress in the enclosure, and lack of need for alteration to animal size variation as it grows. However, animals' voluntary movements, which have no relation to the startles evoked by acoustic stimuli, are problematic, as they cannot be excluded in the case of the unconstrained enclosure based GPIAS measurement system. In order to discount voluntary movements which are not associated with external acoustic stimuli, we propose the conditional random inter-stimulus interval (CR ISI) method for unconstrained enclosure based GPIAS measurement. With the proposed ISI method, the unconstrained enclosure based acoustic startle response measurement system has been implemented in this paper. As a result, the effectiveness of the proposed CR ISI method has been verified and compared with those of conventional ISI methods through animal experiments using SD-rats. The experimental results showed that abnormal startle responses and invalid GPIAS values caused by motion were prevented when our proposed CR ISI method was applied to our implemented system. It was also verified that our proposed CR ISI method is advantageous in reducing the total experimental time for acquiring normal startle responses and valid GPIAS values, compared to conventional ISI methods, since our proposed CR ISI can begin the acoustic stimulation only when the animal gets stable and motionless.

Numerical error monitoring.

Error monitoring has recently been discovered to have informationally rich foundations in the timing domain. Based on the common properties of magnitude-based representations, we hypothesized that judgments on the direction and the magnitude of errors would also reflect their objective counterparts in the numerosity domain. In two experiments, we presented fast sequences of "beeps" with random interstimulus intervals and asked participants to stop the sequence when they thought the target count (7, 11, or 19) had been reached. Participants then judged how close to the target they stopped the sequence, and whether their response undershot or overshot the target. Individual linear regression fits as well as the linear mixed model with a fixed effect of reproduced numerosity on confidence ratings, and participants as independent random effects on the intercept and the slope, revealed significant positive slopes for all the target numerosities. Our results suggest that humans can keep track of the direction and degree of errors in the estimation of discrete quantities, pointing at a numerical-error-monitoring ability.

Adaptive flexibility of the within-hand attentional gradient in touch: An MEG study

Previous studies have demonstrated the cortical mechanisms for the gradient of spatial attention in vision and audition, whereas those for touch have yet to be elucidated in detail. In order to examine the within-hand gradient of tactile spatial attention in the cerebral cortex, we used magnetoencephalography (MEG) to record cortical responses to an electrocutaneous stimulation presented randomly to any of the five fingers of the right hand at a random interstimulus interval (750–1250 ms). Participants attended to the index finger, ring finger, or both to detect a rare target stimulus in a sequence of frequent standard stimuli presented to the attended finger(s) by silent counting. Neuromagnetic responses around the contralateral primary and secondary somatosensory cortices (SIc and SIIc) at 50–70 ms and 80–100 ms, respectively, for the stimulation of the index or ring finger were stronger when that finger was attended than when the distant finger was attended or at rest. The amplitude of the SIIc response was also intermediate when the index and ring fingers were simultaneously attended. The SIIc response to the task-irrelevant stimulation of the thumb or little finger increased when the index or ring finger was attended, respectively, suggesting an across-finger gradient of tactile attention. Simultaneous attention to the index and ring fingers decreased the SIIc response to the task-irrelevant stimulation of the intervening middle finger more than that with attention to either one of the two fingers. The earliest attentional sign was observed for the SI M40c response, with the amplitude increasing with the stimulation of the unattended finger. Furthermore, late responses in the temporo-parietal junction (TPJ) and prefrontal cortex (PFC) were stronger with the stimulation of the unattended finger than with that of the attended finger. Thus, the present study provides cortical evidence for the adaptive control of the within-hand, across-finger gradient of tactile attention that depends on whether attention is focused on a single finger or divided into non-adjacent different fingers.

Emotion-Related Consciousness Detection in Patients With Disorders of Consciousness Through an EEG-Based BCI System.

For patients with disorders of consciousness (DOC), such as vegetative state (VS) and minimally conscious state (MCS), detecting and assessing the residual cognitive functions of the brain remain challenging. Emotion-related cognitive functions are difficult to detect in patients with DOC using motor response-based clinical assessment scales such as the Coma Recovery Scale-Revised (CRS-R) because DOC patients have motor impairments and are unable to provide sufficient motor responses for emotion-related communication. In this study, we proposed an EEG-based brain-computer interface (BCI) system for emotion recognition in patients with DOC. Eight patients with DOC (5 VS and 3 MCS) and eight healthy controls participated in the BCI-based experiment. During the experiment, two movie clips flashed (appearing and disappearing) eight times with a random interstimulus interval between flashes to evoke P300 potentials. The subjects were instructed to focus on the crying or laughing movie clip and to count the flashes of the corresponding movie clip cued by instruction. The BCI system performed online P300 detection to determine which movie clip the patients responsed to and presented the result as feedback. Three of the eight patients and all eight healthy controls achieved online accuracies based on P300 detection that were significantly greater than chance level. P300 potentials were observed in the EEG signals from the three patients. These results indicated the three patients had abilities of emotion recognition and command following. Through spectral analysis, common spatial pattern (CSP) and differential entropy (DE) features in the delta, theta, alpha, beta, and gamma frequency bands were employed to classify the EEG signals during the crying and laughing movie clips. Two patients and all eight healthy controls achieved offline accuracies significantly greater than chance levels in the spectral analysis. Furthermore, stable topographic distribution patterns of CSP and DE features were observed in both the healthy subjects and these two patients. Our results suggest that cognitive experiments may be conducted using BCI systems in patients with DOC despite the inability of such patients to provide sufficient behavioral responses.

S142. Attentional gradient in touch: An MEG study

Introduction Previous studies have demonstrated the cortical mechanisms for the gradient of spatial attention in vision and audition, whereas those for touch have yet to be elucidated in detail. We used magnetoencephalography (MEG) to examine the within-hand gradient of tactile spatial attention in the cerebral cortex. Methods We recorded cortical responses to an electrocutaneous stimulation presented randomly to any of the five fingers of the right hand at a random interstimulus interval (750–1250 ms). Participants attended to the index finger, ring finger, or both to detect a rare target stimulus presented there by silent counting. Results Neuromagnetic responses around the contralateral primary and secondary somatosensory cortices (SIc and SIIc) for the stimulation of the index or middle finger were stronger when that finger was attended than when the distant finger was attended. The SIIc response to the task-irrelevant stimulation of the thumb or little finger increased when the index or ring finger was attended, respectively, suggesting an across-finger gradient of tactile attention. Simultaneous attention to the index and ring fingers decreased the SIIc response to the task-irrelevant stimulation of the intervening middle finger more than that with attention to either one of the two fingers. Furthermore, late responses in the temporo-parietal junction (TPJ) and prefrontal cortex (PFC) were stronger with the stimulation of the unattended finger than with that of the attended finger. Conclusion The present study provides cortical evidence for the adaptive control of the within-hand, across-finger gradient of tactile attention that depends on whether attention is focused on a single finger or divided into non-adjacent different fingers.

0227 Sleep Deprivation Enlarges Inter-stimulus Interval Effect On Vigilant Attention

Sleep deprivation (SD) significantly impairs vigilance attention and reduces the ability to maintain a consistent alertness level. The Psychomotor Vigilance Test (PVT) is a widely used and highly sensitive vigilance task for sleep studies, which records reaction times (RT) to visual stimuli that occurs at random inter-stimulus intervals (ISI). Previous studies have shown that longer ISI facilitates faster RT on the PVT. Although the negative effects of sleep loss on PVT performance have been well documented, whether and how SD modulates the ISI effect on vigilant attention remain elusive. Here we studied this question using a large PVT data set. Seventy health adults (33.9 ± 8.8y, 41 males) participated in a 5-day and 4-night in-laboratory controlled sleep study, including n=54 in the experimental group involving 36-hour of acute total SD (TSD) followed by two nights of recovery sleep, and n=16 in the control group without SD. All participants completed a cognitive test battery every 2 hours while awake, including a 10-min standard PVT and a 3-min brief PVT (PVT-B). A total of 1766 PVT and 1622 PVT-B tests data were included. The linear approach to threshold with ergodic rate (LATER) model was used to fit the data. Reliable effects of ISI on vigilant attention were found for the PVT and PVT-B in both experimental and control groups, such that RT decreased monotonically with longer ISI. The LATER model indicated that changes in perceptual sensitivity rather than threshold adjustment may underlie this ISI effect. A larger ISI effect was found for PVT tests after TSD compared to those after baseline or recovery sleep (p<0.001), whereas no differences were found between PVT tests after baseline or recovery sleep in the SD group, nor among PVT tests on different days in the control group. Our results suggest that sleep deprivation increases the ISI effect on both standard 10-min and brief 3-min PVT, which may be due to altered perceptual sensitivity of time intervals after sleep loss. Supported in part by NIH grants R01-HL102119, R01-MH107571, R01-NR004281, and CTRC UL1RR024134.

11. Excessive inhibitory visuomotor connections in Parkinson’s disease with freezing of gait

Objectives Freezing of gait (FoG) is an invalidating symptom in patients with Parkinson’s disease (PD); it is defined as a brief, episodic absence or marked reduction of forward progression of the feet despite the intention to walk. The pathophysiology of this phenomenon remains obscure. Visual information are crucial for the initiation and control of movement, therefore an impairment of the visuomotor connections may underlie FoG. We used transcranial magnetic stimulation (TMS) to assess bilateral physiological connections (VMc) between primary visual (V1) and motor (M1) areas in PD with (PD + FoG) and without FoG (PD-FoG).We hypothesized that PD+FoG would show an abnormal response in M1. Methods Twelve PD+FoG were compared with 12 PD-FoG and 12 healthy subjects (HS) of similar age and sex. VMc was assessed bilaterally in resting participants by delivering a conditioning stimulus (CS) over the phosphene hotspot of V1 (intensity 90% phosphene threshold, PT) followed at two random interstimulus intervals (ISIs) (18 and 40 ms) by a test stimulus (TS) over left and right M1 to elicit a motor evoked potential (MEP) of ∼1 mV from the controlateral first dorsal interosseous (FDI). Results In HS, the VMc was reproducible with MEP suppression at ISI of 18 and 40 ms. Similar effects occurred in PD-FoG. PD+FoG behaved differently, since the inhibitory VMc was significantly enhanced in the right, non-dominant hemisphere. Conclusions PD+FoG had an excessive inhibitory response of the right M1 to inputs travelling from V1. Significance This may represent one core factor for the pathophysiology of FoG.

O158 Excessive inhibitory visuomotor connections in parkinson’s disease with freezing of gait

Freezing of gait (FoG) is an invalidating symptom in patients with Parkinson’s disease (PD); it is defined as a brief, episodic absence or marked reduction of forward progression of the feet despite the intention to walk. The pathophysiology of this phenomenon remains obscure. Visual information are crucial for the initiation and control of movement, therefore an impairment of the visuomotor connections may underlie FoG. We used transcranial magnetic stimulation (TMS) to assess bilateral physiological connections (VMc) between primary visual (V1) and motor (M1) areas in PD with (PD + FoG) and without FoG (PD-FoG).We hypothesized that PD+FoG would show an abnormal response in M1. Twelve PD+FoG were compared with 12 PD-FoG and 12 healthy subjects (HS) of similar age and sex. VMc was assessed bilaterally in resting participants by delivering a conditioning stimulus (CS) over the phosphene hotspot of V1 (intensity 90% phosphene threshold, PT) followed at two random interstimulus intervals (ISIs) (18 and 40 ms) by a test stimulus (TS) over left and right M1 to elicit a motor evoked potential (MEP) of ∼1 mV from the controlateral first dorsal interosseous (FDI). In HS, the VMc was reproducible with MEP suppression at ISI of 18 and 40 ms. Similar effects occurred in PD-FoG. PD+FoG behaved differently, since the inhibitory VMc was significantly enhanced in the right, non-dominant hemisphere. PD+FoG had an excessive inhibitory response of the right M1 to inputs travelling from V1. This may represent one core factor for the pathophysiology of FoG.

Decoding fMRI events in sensorimotor motor network using sparse paradigm free mapping and activation likelihood estimates.

Most functional MRI (fMRI) studies map task-driven brain activity using a block or event-related paradigm. Sparse paradigm free mapping (SPFM) can detect the onset and spatial distribution of BOLD events in the brain without prior timing information, but relating the detected events to brain function remains a challenge. In this study, we developed a decoding method for SPFM using a coordinate-based meta-analysis method of activation likelihood estimation (ALE). We defined meta-maps of statistically significant ALE values that correspond to types of events and calculated a summation overlap between the normalized meta-maps and SPFM maps. As a proof of concept, this framework was applied to relate SPFM-detected events in the sensorimotor network (SMN) to six motor functions (left/right fingers, left/right toes, swallowing, and eye blinks). We validated the framework using simultaneous electromyography (EMG)-fMRI experiments and motor tasks with short and long duration, and random interstimulus interval. The decoding scores were considerably lower for eye movements relative to other movement types tested. The average successful rate for short and long motor events were 77 ± 13% and 74 ± 16%, respectively, excluding eye movements. We found good agreement between the decoding results and EMG for most events and subjects, with a range in sensitivity between 55% and 100%, excluding eye movements. The proposed method was then used to classify the movement types of spontaneous single-trial events in the SMN during resting state, which produced an average successful rate of 22 ± 12%. Finally, this article discusses methodological implications and improvements to increase the decoding performance. Hum Brain Mapp 38:5778-5794, 2017. © 2017 Wiley Periodicals, Inc.

23. Visuo-motor connectivity in photosensitive epilepsies

Objective Visual and motor cortex are involved in the origin/propagation of the photoparoxysmal response (PPR), a stronghold for the diagnosis of generalized photosensitive epilepsies. The study of the functional connection between these two distant areas with transcranial magnetic stimulation (TMS), could help clarify the pathophysiology of photosensitivity. Methods Eleven patients with idiopathic generalized epilepsy and photosensitivity were compared to 11 healthy subjects. We measured the resting motor threshold of the left hand motor area and the phosphene threshold. The paradigm consisted in a conditioning stimulus (CS) delivered over the phosphene hotspot of the visual cortex and followed at random interstimulus intervals (15–40 ms) by a test stimulus over the left motor cortex to evoke a motor evoked potential (MEP) of ∼1 mV from right FDI. The conditioned-MEP was expressed as a percentage of the unconditioned-MEP amplitude. Results In healthy subjects the CS over the visual cortex produced significant inhibitory changes on the corticospinal excitability with a time course between 18 and 40 ms. Patients with IGE and photosensitivity showed a failure of the physiological inhibition. Conclusions In photosensitive patients the alteration of the normal visuo-motor functional connectivity could be responsible for the origin/propagation of the PPR from the hyper-excitable visual cortex to the motor cortex.

Pre-Synaptic Inhibition of Afferent Feedback in the Macaque Spinal Cord Does Not Modulate with Cycles of Peripheral Oscillations Around 10 Hz.

Spinal interneurons are partially phase-locked to physiological tremor around 10 Hz. The phase of spinal interneuron activity is approximately opposite to descending drive to motoneurons, leading to partial phase cancellation and tremor reduction. Pre-synaptic inhibition of afferent feedback modulates during voluntary movements, but it is not known whether it tracks more rapid fluctuations in motor output such as during tremor. In this study, dorsal root potentials (DRPs) were recorded from the C8 and T1 roots in two macaque monkeys following intra-spinal micro-stimulation (random inter-stimulus interval 1.5–2.5 s, 30–100 μA), whilst the animals performed an index finger flexion task which elicited peripheral oscillations around 10 Hz. Forty one responses were identified with latency < 5 ms; these were narrow (mean width 0.59 ms), and likely resulted from antidromic activation of afferents following stimulation near terminals. Significant modulation during task performance occurred in 16/41 responses, reflecting terminal excitability changes generated by pre-synaptic inhibition (Wall's excitability test). Stimuli falling during large-amplitude 8–12 Hz oscillations in finger acceleration were extracted, and sub-averages of DRPs constructed for stimuli delivered at different oscillation phases. Although some apparent phase-dependent modulation was seen, this was not above the level expected by chance. We conclude that, although terminal excitability reflecting pre-synaptic inhibition of afferents modulates over the timescale of a voluntary movement, it does not follow more rapid changes in motor output. This suggests that pre-synaptic inhibition is not part of the spinal systems for tremor reduction described previously, and that it plays a role in overall—but not moment-by-moment—regulation of feedback gain.

Overactive visuomotor connections underlie the photoparoxysmal response. A TMS study.

The photoparoxysmal response (PPR) involves rapid spread of epileptic activity from visual to parietal and frontal areas. We used a transcranial magnetic stimulation (TMS) technique to assess the physiologic connections between primary visual (V1) and motor (M1) areas in patients with idiopathic generalized epilepsy (IGE). We hypothesized that in PPR-positive patients, M1 would respond excessively to inputs from V1. Eleven photosensitive patients with IGE who had a PPR at the time of the study were compared with 10 similar patients without a PPR, and with 11 healthy subjects of similar age and sex. The connection between V1 and M1 was assessed in resting participants by delivering a conditioning stimulus (CS) over the phosphene hotspot of the visual cortex (intensity 90% phosphene threshold, PT) followed at random interstimulus intervals (ISIs; 15, 18, 21, 24, 27, 30, 35 and 40 msec) by a test stimulus (TS) over the left motor cortex to elicit a motor evoked potential (MEP) of ~1 mV from the right first dorsal interosseous muscle. In healthy subjects, a CS over V1 suppressed M1 at ISIs between 18 and 40 msec. Similar effects occurred in IGE patients without a PPR. This was not true in PPR-positive IGE patients, in whom this type of physiologic inhibition was significantly (p < 0.05) reduced. IGE patients with a PPR have an overactive functional response of M1 to inputs traveling from V1. This may represent one core factor for the anterior spread of the PPR itself and for the origin of the abnormal epileptic motor phenomenon, such as myoclonus.

Interaction between visual and motor cortex: a transcranial magnetic stimulation study.

The major link between the visual and motor systems is via the dorsal stream pathways from visual to parietal and frontal areas of the cortex. Although the pathway appears to be indirect, there is evidence that visual input can reach the motor cortex at relatively short latency. To shed some light on its neural basis, we studied the visuomotor interaction using paired transcranial magnetic stimulation (TMS). Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous in sixteen healthy volunteers. A conditioning stimulus (CS) was applied over the phosphene hotspot of the visual cortex, followed by a test stimulus over the left primary motor cortex (M1) with a random interstimulus interval (ISI) in range 12-40 ms. The effects of paired stimulation were retested during visual and auditory reaction-time tasks (RT). Finally, we measured the effects of a CS on short-interval intracortical inhibition (SICI). At rest, a CS over the occiput significantly (P < 0.001) suppressed test MEPs with an ISI in the range 18-40 ms. In the visual RT, inhibition with an ISI of 40 ms (but not 18 ms) was replaced by a time-specific facilitation (P < 0.001), whereas, in the auditory RT, the CS no longer had any effect on MEPs. Finally, an occipital CS facilitated SICI with an ISI of 40 ms (P < 0.01). We conclude that it is possible to study separate functional connections from visual to motor cortices using paired-TMS with an ISI in the range 18-40 ms. The connections are inhibitory at rest and possibly mediated by inhibitory interneurones in the motor cortex. The effect with an ISI of 40 ms reverses into facilitation during a visuomotor RT but not an audiomotor RT. This suggests that it plays a role in visuomotor integration.

The Effects of Activation Levels of Visual Long-Term Memory on Visual Short-Term Memory

It is a fundamental question that whether visual short-term memory(VSTM) and visual long-term memory(VLTM) are two separate stores or two different states of the same representation. Previous researches focused on whether VSTM could be facilitated by VLTM, however, existing studies on this topic yielded conflicting results. Most neurophysiological or behavioral studies adopted faces as stimuli, and have arrived at the conclusion that VLTM could facilitate VSTM. It ought to be noted that in studies that found no facilitation, the exposure of the experimental materials was not sufficiently to activate VLTM. Therefore, it was hypothesized that only a highly activated VLTM could facilitate VSTM.The purpose of the present study was to investigate the effect of activation level of VLTM on facilitating VSTM within the change-detection paradigm. In Experiment 1, participants were instructed to memorize a study image including 6 geometric figures(6 random shape-color bindings from a pool of eight shapes and eight colors), and then after a random inter-stimulus interval(1, 1.5, or 3 s), either the same image or an image with one shape or color changed was presented, and participants were asked to judge whether they detected a change. In Experiment 2, a total of 8 geometric figures with fixed combinations of color and shape were used to substitute all the random combinations of experiment 1. The experimental procedure and design was identical to experiment 1. One hour after the experiment, participants were asked to participate in a post-experiment to examine whether the study stimuli were stored in VLTM. In Experiment 3, participants were asked to visually study the 8 figures in experiment 2 for a week(at least 10 min a day). Then, they took part in a pre-experiment(the same as the post-experiment in experiment 2) to test whether a highly activated VLTM was obtained. At last, the experimental procedure as described in Experiment 2 was performed. The results showed that although VLTM was formed in experiment 2, there was no significant increase in d' or K value of VSTM, indicating no facilitation of VLTM in this case. However, in experiment 3, VLTM was highly activated, and a better performance was observed as compared with experiment 1 and 2. In addition, the effect size of ISI decreased as the activation level of VLTM increased from experiment 1 to experiment 3. The results suggest that whether VLTM can facilitate VSTM is mainly depend on the activation level of VLTM, only a highly activated VLTM can facilitate VSTM, and can inhibit the rapid fading of VSTM traces. On this basis, we conclude that VSTM and VLTM are more likely to be two states of the same representation.

28. Visuomotor functional connectivity: A TMS study

The interaction between visual inputs and motor system is of crucial importance in movement control. We studied the functional connectivity between visual and motor cortex by means of transcranial magnetic stimulation. Sixteen volunteers (21–51 yrs) participated in this study. We measured resting motor threshold (RMT) of the hand motor area and phosphene threshold (PT). A conditioning stimulus (CS) delivered over visual cortex at different intensities (80 and 90% PT) was followed at random interstimulus intervals (ISIs) (12, 15, 18, 21, 24, 27, 30, 35 and 40 ms) by a test stimulus (TS) over left motor cortex to evoke a motor evoked potential (MEP) of ∼1 mV from right FDI. The conditioned-MEP was expressed as a percentage of the unconditioned-MEP amplitude. One-way ANOVAs analyzed the effects of the CS with “ISIs” as main factor. ANOVA showed a main effect of ISI when the CS intensity was 80% PT ( F (9, 90) = 3.410, p = 0.001) and 90% PT ( F (9, 99) = 3.081, p = 0.003). Post hoc analysis confirmed that the size of the conditioned-MEP was significantly reduced at 18, 21, 24, 40 ms ( p < 0.05) with 80% PT, and significantly reduced at 18, 21, 27, 30, 35, 40 ms ( p < 0.02) with 90% PT. In subjects at rest, conditioning stimuli over the visual cortex produce inhibitory changes on corticospinal excitability with a time course between 18 and 40 ms.

Long-Range, Pattern-Dependent Contextual Effects in Early Human Visual Cortex

The standard view of neurons in early visual cortex is that they behave like localized feature detectors. Here we demonstrate that processing in early visual areas goes beyond feature detection by showing that neural responses are greater when a feature deviates from its context compared to when it does not deviate from its context. Using psychophysics, fMRI, and electroencephalography methodologies, we measured neural responses to an oriented Gabor ("target") embedded in various visual patterns as defined by the relative orientation of flanking stimuli. We first show using psychophysical contrast adaptation and fMRI that a target that differs from its context results in more neural activity compared to a target that is contained within an alternating sequence, suggesting that neurons in early visual cortex are sensitive to large-scale orientation patterns. Next, we use event-related potentials to show that orientation deviations affect the earliest sensory components of the target response. Finally, we use forced-choice classification of "noise" stimuli to show that we are more likely to "see" orientations that deviate from the context. Our results suggest that early visual cortex is sensitive to global patterns in images in a way that is markedly different from the predictions of standard models of cortical visual processing.

Dynamics of Within-, Inter-, and Cross-Modal Attentional Modulation

Numerous studies have demonstrated effects of spatial attention within single sensory modalities (within-modal spatial attention) and the effect of directing attention to one sense compared with the other senses (intermodal attention) on cortical neuronal activity. Furthermore, recent studies have been revealing that the effects of spatial attention directed to a certain location in a certain sense spread to the other senses at the same location in space (cross-modal spatial attention). The present study used magnetoencephalography to examine the temporal dynamics of the effects of within-modal and cross-modal spatial and intermodal attention on cortical processes responsive to visual stimuli. Visual or tactile stimuli were randomly presented on the left or right side at a random interstimulus interval and subjects directed attention to the left or right when vision or touch was a task-relevant modality. Sensor-space analysis showed that a response around the occipitotemporal region at around 150 ms after visual stimulation was significantly enhanced by within-modal, cross-modal spatial, and intermodal attention. A later response over the right frontal region at around 200 ms was enhanced by within-modal spatial and intermodal attention, but not by cross-modal spatial attention. These effects were estimated to originate from the occipitotemporal and lateral frontal areas, respectively. Thus the results suggest different spatiotemporal dynamics of neural representations of cross-modal attention and intermodal or within-modal attention.