Manipulating intent: evidence for a causal role of the superior colliculus in target selection

The superior colliculus (SC) is well known for its role in the motor control of saccades. Recent work has shown that it also plays a role in the selection of saccades, but a causal role in the process of target selection has not been demonstrated. We applied subthreshold microstimulation to the SC while monkeys performed a task requiring them to select a stimulus as the target for a pursuit or saccade movement. Stimulation increased the proportion of selections toward the stimulus that appeared contralateral to the site of stimulation and also decreased their latencies. For pursuit, this stimulation-induced contralateral response bias was with respect to the initial target location and not the direction of eye movement, demonstrating a causal effect on target choice distinct from any effect on motor preparation. These results show that the SC helps decide the object of the next movement, beyond its traditional responsibility of saccade production.     

Dynamics of the electroencephalogram during performance of a mental task

Dynamics of the EEG activity — during the performance of a mental task — was investigated by the nonstationary power spectrum method. The performance of the mental arithmetic is associated with suppression of the alpha wave. The suppression of the alpha wave is not as marked as the alpha blocking accompanying opening of the eyes. Alpha wave suppression during the mental task was nonsymmetric around the center frequency of the alpha wave, and lower frequency components were suppressed more than high frequency components. An explanation of these observations is proposed in terms of decrease in the periods of alpha prevalence during performance of mental tasks.     

Topography of visual event-related potentials during geometric and phonetic discriminations

Event-related potentials (ERPs) were obtained to letters during 3 tasks that involved a SIMPLE RESPONSE (SR) to each letter presentation, a FORM discrimination of the letters that formed a closed loop, and a RHYME discrimination of the letters that rhymed with the letter ‘v’. The first task only required detection of the letters, the FORM task required a visual-spatial analysis. and the RHYME task, a grapheme-phoneme conversion of the letters followed by a determination of rhyming characteristics. The SR ERPs were morphologically different from the discriminative ERPs, notably by the absence of N2 and P3. The difference wave forms between the discrimination and SR conditions and between the targets and non-targets indicated differential topographies of components associated with the FORM and RHYME tasks in the 300 msec latency region. In both of these tasks, components exhibited distributions localized primarily in the occipital regions, whereas in the RHYME task they extended more anteriorly and encompassed temporo-parietal regions. Thus, although the stimulus presentation was visual, the requirement of a visual-auditory conversion in the RHYME task resulted in activity that was more proximal to auditory regions than when only a FORM analysis of the letters was required.     

Evaluation of mental task strain based on occipital beta activity and subjective rating of task difficulty

Occipital midline beta-2 (Oz beta 2) amplitudes and subjective ratings of task difficulty were measured in 24 healthy male students, aged 19-23 years, performing four kinds of mental task (transcribing, cancelling, adding, and calculating) at two grades of self-pace (maximum workload and moderate workload) for 5 min each. Significant differences in Oz beta 2 amplitudes were observed between the tasks at either workload, except between the adding task and the calculating task. However no significant difference in the subjective ratings was observed between the tasks at either workload, except between the adding task and the calculating task or the cancelling task at maximum workload. Thus the Oz beta 2 amplitude was more sensitive to differentiation of task strain between the mental tasks, than the subjective rating. In comparison with the critical levels deduced previously, it was estimated from the Oz beta 2 amplitudes that all the tasks at either workload could induce heavy task strain in the subject, except for the cancelling task at moderate workload. From the subjective ratings, however, it was estimated that no task could induce heavy task strain in the subject. It was, moreover, suggested that the Oz beta 2 amplitudes reflected the difference in the quality of cortical functions and that the subjective ratings of task difficulty were associated with time pressure rather than the quality of cortical functions.     

Readiness to respond in a target detection task: pre- and post-stimulus event-related potentials in normal subjects

Brain potentials were recorded from 12 normal subjects engaged in an auditory target detection task (target stimulus probability of 0.2, stimulus rate of 1 every 2 sec) when instructions were (1) to press a response button with the thumb of the dominant hand to each target or (2) to keep a mental count of each target. A pre-stimulus slow negative potential was identified before every stimulus except non-targets immediately after targets. The amplitude of the pre-stimulus negativity was significantly affected by task instructions and was up to 4 times larger during the button press than the mental count condition. In contrast, the amplitudes and latencies of the event-related components (N100, P200, N200 and P300), when slow potentials were removed by filtering, were not different as a function of press or count instructions. The immediately preceding stimulus sequence affected both the amplitude and onset latency of the pre-stimulus negativity; both measures increased as the number of preceding non-targets increased. The amplitude of the pre-stimulus negative shift to targets also increased significantly as RT speed decreased. The major portion of the pre-stimulus negative potential is considered a readiness potential (RP) reflecting preparations to make a motor response. The amplitude of the RP during the target detection task did not significantly lateralize in contrast to the RP accompanying self-paced movements.     

Cardiovascular reactivity to mental stress: relationship with menstrual cycle and gender

The purpose of the present study was to determine the fluctuation in cardiovascular reactivity to mental stress during the menstrual cycle by comparing heart rate variability (HRV), and other physiological and psychological data in females with those in males. Cardiovascular reactivity to two mental tasks was measured in 14 females during the follicular and luteal phase of menstruation over two menstrual cycles. The same tasks were subsequently given to a matched pair of males (N=14), at the same intervals as their corresponding females. Heart rate, blood pressure and HRV were used as indices of cardiovascular reactivity. Subjective mental workload was measured at the end of each task. Power spectral analysis of HRV showed that the high frequency (HF) component in HRV decreased more during the luteal phase than the follicular phase. The low frequency (LF) component in HRV and the LF/HF ratio in the luteal phase were significantly higher than that in the follicular phase. The LF component and the LF/HF ratio were significantly lower in females than in males; conversely, the HF component was significantly higher in females than in males. Neither significant effects of menstrual cycle, gender and mental stress nor any significant interactions were found for mental workload. These findings indicate that sympathetic nervous activity in the luteal phase is significantly greater than in the follicular phase whereas parasympathetic nervous activity is predominant in the follicular phase. The results also suggest that predominance of sympathetic nervous activity in males compared with a dominant parasympathetic nervous activity in females.     

Dual Task Performance in Normal Aging: A Comparison of Choice Reaction Time Tasks

This study examined dual task performance in 28 younger (18–30 years) and 28 older (>60 years) adults using two sets of choice reaction time (RT) tasks paired with digit tasks. Set one paired simple choice RT with digit forward; set two paired complex choice RT with digit backward. Each task within each set had easy and hard conditions. For the simple choice RT, participants viewed single letters and pressed a specified keyboard key if the letter was X or Z or a different key for other letters (easy). For the hard condition, there were 4 target letters (X, Z, O, Y). Digit forward consisted of 4 (easy) or 5 (hard) digits. For the complex choice RT, participants viewed 4×4 matrices of Xs and Os, and indicated whether four Xs (easy) or four Xs or four Os (hard) appeared in a row. Digit backward consisted of 3 (easy) or 4 (hard) digits. Within each set, participants performed every possible combination of tasks. We found that in the simple choice RT tasks older adults were significantly slower than, but as accurate as younger adults. In the complex choice RT tasks, older adults were significantly less accurate, but as fast as younger adults. For both age groups and both dual task sets, RT decreased and error rates increased with greater task difficulty. Older adults had greater dual task costs for error rates in the simple choice RT, whereas in the complex choice RT, it was the younger group that had greater dual task costs. Findings suggest that younger and older adults may adopt differential behavioral strategies depending on complexity and difficulty of dual tasks.     

Estimation of mental effort in learning visual search by measuring pupil response

Perceptual learning refers to the improvement of perceptual sensitivity and performance with training. In this study, we examined whether learning is accompanied by a release from mental effort on the task, leading to automatization of the learned task. For this purpose, we had subjects conduct a visual search for a target, defined by a combination of orientation and spatial frequency, while we monitored their pupil size. It is well known that pupil size reflects the strength of mental effort invested in a task. We found that pupil size increased rapidly as the learning proceeded in the early phase of training and decreased at the later phase to a level half of its maximum value. This result does not support the simple automatization hypothesis. Instead, it suggests that the mental effort and behavioral performance reflect different aspects of perceptual learning. Further, mental effort would be continued to be invested to maintain good performance at a later stage of training.     

Prospective memory mediated by interoceptive accuracy: a psychophysiological approach

Previous studies on prospective memory (PM), defined as memory for future intentions, suggest that psychological stress enhances successful PM retrieval. However, the mechanisms underlying this notion remain poorly understood. We hypothesized that PM retrieval is achieved through interaction with autonomic nervous activity, which is mediated by the individual accuracy of interoceptive awareness, as measured by the heartbeat detection task. In this study, the relationship between cardiac reactivity and retrieval of delayed intentions was evaluated using the event-based PM task. Participants were required to detect PM target letters while engaged in an ongoing 2-back working memory task. The results demonstrated that individuals with higher PM task performance had a greater increase in heart rate on PM target presentation. Also, higher interoceptive perceivers showed better PM task performance. This pattern was not observed for working memory task performance. These findings suggest that cardiac afferent signals enhance PM retrieval, which is mediated by individual levels of interoceptive accuracy.This article is part of the themed issue ‘Interoception beyond homeostasis: affect, cognition and mental health’.     

Aging and the time and frequency structure of force output variability.

The present study examined the time and frequency structure of force output in adult humans to determine whether the changes in complexity with age are dependent on external task demands. Healthy young (20-24 yr), old (60-69 yr), and older-old (75-90 yr) humans produced isometric force contractions to constant and sine wave targets that also varied in force level. First, force variability on each force task increased with advancing age. Second, both time and frequency analysis showed that the structure of the force output in the old and older-old adults was less complex in the constant-force level task and more complex in the sine wave force task. Third, the alterations in force output with aging were primarily due to low-frequency bands <4 Hz. These results support the postulation that the observed increase or decrease in physiological complexity with aging is influenced by the relatively fast time scale of external task demands (Vaillancourt DE and Newell KM. Neurobiol Aging 23: 1-11, 2002).     

Blood pressure dipping and salivary cortisol as markers of fatigue and sleep deprivation in staff anesthesiologists

Anesthesiologists often work extended duty shifts that result in acute and chronic sleep loss and circadian disruption. Stress caused by sleep deprivation, together with excessive workload could contribute to acute increases in blood pressure (BP) and sympathetic nervous system activity. Non-dipping pattern of BP is considered an additional risk factor for cardiovascular events and target organ damage. We hypothesized that there would be significant changes of cardiovascular parameters when comparing work on call during the 24-hour in-hospital shift (24-HD) versus ordinary working day (8-HD) combined with changes of dipping pattern and altered diurnal cortisol secretion, measured by salivary cortisol (SC). Following local Medical Ethics Committee approval, 12 out of 36 staff anesthesiologists (8 male, 4 female), 33-61 years old, participated in this study. Ambulatory BP monitor was used for noninvasive 24-hour ambulatory BP and heart rate (HR) monitoring. Each participant was monitored continuously during the 8-HD, as well as during the 24-HD. Saliva for analysis of cortisol levels was collected six times a day (at 8 am, 11 am, 2 pm, 5pm, 8pm, and 11 pm) both during 8-HD and on 24-HD. There was a significant decrease in number of diastolic dippers on call vs. diastolic dippers on ordinary working day (4/12 vs. 10/12, p=0.036), and non significant decrease of systolic dippers (3/12 vs. 7/12, p =0.214). There were no significant differences in SC values between 8-HD and 24-HD at all observed time points. However, the SC values measured during the night were markedly elevated on both days compared with reference values and the shapes of SC curves were altered. The lack of diastolic BP dipping could be more sensitive indicator of stress among staff anesthesiologists than systolic BP dipping. The shape of SC diurnal curve in terms of elevated night values could be another indicator of their chronic fatigue.     

Temporal Constraints of Behavioral Inhibition: Relevance of Inter-stimulus Interval in a Go-Nogo Task

The capacity to inhibit prepotent and automatic responses is crucial for proper cognitive and social development, and inhibitory impairments have been considered to be key for some neuropsychiatric conditions. One of the most used paradigms to analyze inhibitory processes is the Go-Nogo task (GNG). This task has been widely used in psychophysical and cognitive EEG studies, and more recently in paradigms using fMRI. However, a technical limitation is that the time resolution of fMRI is poorer than that of the EEG technique. In order to compensate for these temporal constraints, it has become common practice in the fMRI field to use longer inter-stimulus intervals (ISI) than those used in EEG protocols. Despite the noticeable temporal differences between these two techniques, it is currently assumed that both approaches assess similar inhibitory processes. We performed an EEG study using a GNG task with both short ISI (fast-condition, FC, as in EEG protocols) and long ISI (slow-condition, SC, as in fMRI protocols). We found that in the FC there was a stronger Nogo-N2 effect than in the SC. Moreover, in the FC, but not in the SC, the number of preceding Go trials correlated positively with the Nogo-P3 amplitude and with the Go trial reaction time; and negatively with commission errors. In addition, we found significant topographical differences for the Go-P3 elicited in FC and SC, which is interpreted in terms of different neurotransmitter dynamics. Taken together, our results provide evidence that frequency of stimulus presentation in the GNG task strongly modulates the behavioral response and the evoked EEG activity. Therefore, it is likely that short-ISI EEG protocols and long-ISI fMRI protocols do not assess equivalent inhibitory processes.     

Investigating neural efficiency of elite karate athletes during a mental arithmetic task using EEG

Neural efficiency is proposed as one of the neural mechanisms underlying elite athletic performances. Previous sports studies examined neural efficiency using tasks that involve motor functions. In this study we investigate the extent of neural efficiency beyond motor tasks by using a mental subtraction task. A group of elite karate athletes are compared to a matched group of non-athletes. Electroencephalogram is used to measure cognitive dynamics during resting and increased mental workload periods. Mainly posterior alpha band power of the karate players was found to be higher than control subjects under both tasks. Moreover, event related synchronization/desynchronization has been computed to investigate the neural efficiency hypothesis among subjects. Finally, this study is the first study to examine neural efficiency related to a cognitive task, not a motor task, in elite karate players using ERD/ERS analysis. The results suggest that the effect of neural efficiency in the brain is global rather than local and thus might be contributing to the elite athletic performances. Also the results are in line with the neural efficiency hypothesis tested for motor performance studies.     

Electromyographic data do not support a progressive recruitment of muscle fibers during exercise exhibiting a VO2 slow component

The origin of the slow component (SC) of oxygen uptake kinetics, presenting during exercise above the ventilatory threshold (VT), remains unclear. Possible physiologic mechanisms include a progressive recruitment of type II muscle fibers. The purpose of this study was to examine alterations in muscle activity through electromyography (EMG) and mean power frequency (MPF) analysis during heavy cycling exercise. Eight trained cyclists (mean +/- S.E.; age = 30 +/- 3 years, height = 1771 +/- 4 cm, weight = 73.8 +/- 6.5 kg, VO2max = 4.33 +/- 0.28 l min(-1)) completed transitions from 20W to a workload equaling 50% of the difference between V(T) and VO2max. VO2 was monitored using a breath-by-breath measurement system, and EMG data were gathered from surface electrodes placed on the gastrocnemius lateralis and vastus lateralis oblique. Breath-by-breath data were time aligned, averaged, interpolated to 1-s intervals, and modeled with non-linear regression. Mean power frequency (MPF) and RMS EMG values were calculated for each minute during the exercise bout. Additionally, MPF was determined using both isolated EMG bursts and complete pedal revolutions. All subjects exhibited a VO2 SC (mean amplitude = 0.98 +/- 0.16 l min(-1)), yet no significant differences were observed during the exercise bout in MPF or RMS EMG data (p > 0.05) using either analysis technique. While it is possible that the sensitivity of EMG may be insufficient to identify changes in muscle activity theorized to affect the VO2 SC, the data indicated no relationship between MPF/EMG and the SC during heavy cycling.     

Late divergence of target and nontarget ERPs in a visual oddball task

Different mental operations were expected in the late phase of intracerebral ERPs obtained in the visual oddball task with mental counting. Therefore we searched for late divergences of target and nontarget ERPs followed by components exceeding the temporal window of the P300 wave. Electrical activity from 152 brain regions of 14 epileptic patients was recorded by means of depth electrodes. Average target and nontarget records from 1800 ms long EEG periods free of epileptic activity were compared. Late divergence preceded by almost identical course of the target and nontarget ERPs was found in 16 brain regions of 6 patients. The mean latency of the divergence point was 570+/-93 ms after the stimulus onset. The target post-divergence section of the ERP differed from the nontarget one by opposite polarity, different latency of the components, or even different number of the components. Generators of post-divergence ERP components were found in the parahippocampal gyrus, superior, middle and inferior temporal gyri, amygdala, and fronto-orbital cortex. Finding of late divergence indicates that functional differences exist even not sooner than during the final phase of the task.     

Making the Invisible Visible: Verbal but Not Visual Cues Enhance Visual Detection

Background

Can hearing a word change what one sees? Although visual sensitivity is known to be enhanced by attending to the location of the target, perceptual enhancements of following cues to the identity of an object have been difficult to find. Here, we show that perceptual sensitivity is enhanced by verbal, but not visual cues.

Methodology/Principal Findings

Participants completed an object detection task in which they made an object-presence or -absence decision to briefly-presented letters. Hearing the letter name prior to the detection task increased perceptual sensitivity (d′). A visual cue in the form of a preview of the to-be-detected letter did not. Follow-up experiments found that the auditory cuing effect was specific to validly cued stimuli. The magnitude of the cuing effect positively correlated with an individual measure of vividness of mental imagery; introducing uncertainty into the position of the stimulus did not reduce the magnitude of the cuing effect, but eliminated the correlation with mental imagery.

Conclusions/Significance

Hearing a word made otherwise invisible objects visible. Interestingly, seeing a preview of the target stimulus did not similarly enhance detection of the target. These results are compatible with an account in which auditory verbal labels modulate lower-level visual processing. The findings show that a verbal cue in the form of hearing a word can influence even the most elementary visual processing and inform our understanding of how language affects perception.     

A frequency-weighted method combined with Common Spatial Patterns for electroencephalogram classification in brain–computer interface

Common Spatial Patterns (CSP) has been proven to be a powerful and successful method in the detection of event-related desynchronization (ERD) and ERD based brain–computer interface (BCI). However, frequency optimization combined with CSP has only been investigated by a few groups. In this paper, a frequency-weighted method (FWM) is proposed to optimize the frequency spectrum of surface electroencephalogram (EEG) signals for a two-class mental task classification. This straightforward method computes a weight value for each frequency component according to its importance for the discrimination task and reforms the spectrum with the computed weights. The off-line analysis shows that the proposed method achieves an improvement of about 4% (averaged over 24 datasets) in terms of cross-validation accuracy over the basic CSP.     

Iterative Fragmentation of Cognitive Maps in a Visual Imagery Task

It remains unclear whether spontaneous eye movements during visual imagery reflect the mental generation of a visual image (i.e. the arrangement of the component parts of a mental representation). To address this specificity, we recorded eye movements in an imagery task and in a phonological fluency (non-imagery) task, both consisting in naming French towns from long-term memory. Only in the condition of visual imagery the spontaneous eye positions reflected the geographic position of the towns evoked by the subjects. This demonstrates that eye positions closely reflect the mapping of mental images. Advanced analysis of gaze positions using the bi-dimensional regression model confirmed the spatial correlation of gaze and towns’ locations in every single individual in the visual imagery task and in none of the individuals when no imagery accompanied memory retrieval. In addition, the evolution of the bi-dimensional regression’s coefficient of determination revealed, in each individual, a process of generating several iterative series of a limited number of towns mapped with the same spatial distortion, despite different individual order of towns’ evocation and different individual mappings. Such consistency across subjects revealed by gaze (the mind’s eye) gives empirical support to theories postulating that visual imagery, like visual sampling, is an iterative fragmented processing.     

Frequency analysis of electromyographically measured covert speech behavior

Eleven subjects were asked to silently read slides of the letters "P" and "T," and to view meaningless control slides similarly as they were presented visually. One-eighth-second electromyographic excerpts were sampled from the baseline and response periods. The data were then transformed into the frequency domain for inferential analyses. The mean power spectral frequencies for the response period were significantly lower than those for the base-line in the overall analysis. There were, however, no significant changes from baseline as a function of kind of stimulus (T, P, or Control) or muscle activated (lips or tongue). It was concluded that there was a generalized responding, not unique to the processing of the specific stimuli studied. Frequency analysis of EMG measures of covert behavior holds some promise of yielding unique information not available through traditional analysis procedures, but more sensitive methods than those used here would be required to demonstrate this.     

Alloreactivity against IE-encoded antigens: evidence of the discrepancy between graft rejection and reactivity of IE-reactive T cells.

Participation of IE antigens (Ag) in immune response as the transplantation Ag was examined. IE- B10.A(4R)(4R; Kk, IAk, IE-, Db) mice could not reject skin graft from IE Ag alone-disparate B10.A(2R) (2R; Kk, IAk, IEk, Db) mice despite intravenous (iv) injection of 2R spleen cells (SC) before or after skin grafting, indicating that graft rejection could not be caused across IE Ag-barrier alone. Furthermore, 4R SC could not induce lethal graft-versus-host disease (GVHD) in supralethally (950 rad) irradiated 2R mice. On the other hand, infiltration of lymphoid cells was observed at the site of transplanted 2R skin in 4R mice. SC of 4R mice unprimed or primed with 2R skin or 2R SC showed the capability to proliferate in vitro in response to 2R Ag. In immunofluorescence analysis of lymph node cells (LNC) of 4R mice injected iv with 2R SC 7 days earlier, IE-reactive CD4+Vbeta 11+ T cells did not change in number, but slightly increased the expression of interleukin-2 receptor (IL-2R). In 2R mice irradiated with 670 rad and injected iv with 4R SC 7 days earlier, 4R-derived CD4+V beta 11+ T cells proliferated, changed to blastoid form, and showed a markedly increased expression of IL-2R. To further investigate the influence of IE alloantigens on transplantation immunity, IL-2 production and anti-class I CTL activity were assayed. The 4R SC capable of recognizing IEk and Dk Ag of B10.BR (Kk, IAk, IEk, Dk) generated levels of both IL-2 and CTL activities higher than those of 2R SC capable of recognizing Dk Ag alone. These results strongly suggest that IE alloantigens indirectly act as the transplantation Ag by the stimulation of IE-reactive CD4+ helper T cells resulting in the differentiation of class I-restricted CD8+ T cells.