Reaction times predict dynamic brain representations measured with MEG for only some object categorisation tasks

Categorization is the mental operation by which the brain classifies objects and events. It is classically assessed using semantic and non-semantic matching or sorting tasks. These tasks show a high variability in performance across healthy controls and the cerebral bases supporting this variability remain unknown. In this study we performed a voxel-based morphometry study to explore the relationships between semantic and shape categorization tasks and brain morphometric differences in 50 controls. We found significant correlation between categorization performance and the volume of the gray matter in the right anterior middle and inferior temporal gyri. Semantic categorization tasks were associated with more rostral temporal regions than shape categorization tasks. A significant relationship was also shown between white matter volume in the right temporal lobe and performance in the semantic tasks. Tractography revealed that this white matter region involved several projection and association fibers, including the arcuate fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, and inferior longitudinal fasciculus. These results suggest that categorization abilities are supported by the anterior portion of the right temporal lobe and its interaction with other areas.

THINGS-data reflects three large-scale neuroimaging and behavioral datasets of object processing in humans, comprising densely sampled functional MRI and magnetoencephalographic recordings, as well as 4.70 million similarity judgments in response to thousands of photographic images for up to 1854 objects.

Introduction Few reports have examined how pre-sleep alcohol affects performance on the next day given adequate sleep opportunity on a preferred schedule. Our goal is to identify whether alcohol intake targeting .08g% 1 hr before sleep of ~8 h will affect PVT performance on subsequent days, with the hypothesis that morning performance will be negatively affected. Methods 25 adults (13F; age range 22-57 y) completed the full study, including at-home sleep on a fixed schedule of 8-9 hr and two 3-night in-lab PSG sessions spaced ≥3 days apart. Sessions were counterbalanced for alcoholic or nonalcoholic control beverage administered in 3 drinks over 45 minutes ending 1 hr before bedtime. Alcohol was targeted to .08g%. The 10-min PVT (Ambulatory Monitoring, Inc.) was given each night (PM-Lab) 1.5 hr before drinking and in the morning after a light breakfast (AM-Lab) 50 min after waking. PVT was performed at home/work twice each day within 1.5-h windows starting 3h after waking (AM-Home) and 7.5h after waking (PM-Home). Two reaction time (RT) variables were assessed: RRT (1/RT), FRT (10% fastest RT). Linear mixed effects models were used to account for nesting of assessments within alcohol/control condition and days. Results RRTs showed slowed RT (meanRT±SE) following alcohol: AM-Lab F=7.234, p=.008, alcohol RT=246±9.6 msec, control RT=234±9.6 msec; AM-Home F=17.936, p<.001, alcohol RT=254±9.5 msec, control RT=242±9.6 msec; but not PM-Home or PM-Lab tests. FRT slowed for AM-Lab F=9.391, p=.003, alcohol FRT=195±4.3 msec, control FRT=201±4.3 msec; AM-Home F=17.251, p=.001, alcohol FRT= 202±4.4 msec, control FRT=194±4.4 msec; PM-Home F=3.379, p=.068 (trend), alcohol FR=200±4.8 msec, control FRT=196±4.8 msec, but not for PM-Lab PVTs. PM-Home FRT also had a significant day order effect: F=3.087, p=.0496, Day 1 FRT=197±5.0 msec, Day 2 FRT=202±5.0 msec, Day 3 FRT=195±5.0 msec. Conclusion We found statistically significant slowing of psychomotor vigilance RT on days after pre-sleep alcohol lasting up to 3-4.5h after waking in the morning (with a trend up to 7.5-9h post waking). PVT lapses (not shown) were similarly affected by alcohol. Thus, even with sufficient sleep opportunity, RT is impaired following 3 consecutive nights of alcohol drinking. Support (if any) R01AA025593

The superior temporal sulcus (STS) is a crucial hub for speech perception and can be studied with high spatiotemporal resolution using electrodes targeting mesial temporal structures in epilepsy patients. Goals of the current study were to clarify functional distinctions between the upper (STSU) and the lower (STSL) bank, hemispheric asymmetries, and activity during self-initiated speech. Electrophysiologic properties were characterized using semantic categorization and dialog-based tasks. Gamma-band activity and alpha-band suppression were used as complementary measures of STS activation. Gamma responses to auditory stimuli were weaker in STSL compared with STSU and had longer onset latencies. Activity in anterior STS was larger during speaking than listening; the opposite pattern was observed more posteriorly. Opposite hemispheric asymmetries were found for alpha suppression in STSU and STSL. Alpha suppression in the STS emerged earlier than in core auditory cortex, suggesting feedback signaling within the auditory cortical hierarchy. STSL was the only region where gamma responses to words presented in the semantic categorization tasks were larger in subjects with superior task performance. More pronounced alpha suppression was associated with better task performance in Heschl's gyrus, superior temporal gyrus, and STS. Functional differences between STSU and STSL warrant their separate assessment in future studies.

SummaryThe neural responses that distinguish novel from familiar items in recognition memory tasks are remarkably fast in both humans and nonhuman primates. In humans, the earliest onsets of neural novelty effects emerge at about ∼150–200 ms after stimulus onset [1–5]. However, in recognition memory studies with nonhuman primates, novelty effects can arise at as early as 70–80 ms [6, 7]. Here, we address the possibility that this large species difference in onset latencies is caused experimentally by the necessity of using reward reinforcement to motivate the detection of novel or familiar items in nonhuman primates but not in humans. Via magnetoencephalography in humans, we show in two experiments that the onset of neural novelty signals is accelerated from ∼200 ms to ∼85 ms if correct recognition memory for either novel or familiar items is rewarded. Importantly, this acceleration is independent of whether the detection of the novel or the familiar scenes is rewarded. Furthermore, this early novelty effect contributed to memory retrieval because neural reward responses, which were contingent upon novelty detection, followed ∼100 ms later. Thus, under the contextual influence of reward motivation, behaviorally relevant novelty signals emerge much faster than previously held possible in humans.

Greater cognitive ability in childhood is associated with increased longevity, and speedier reaction time (RT) might account for much of this linkage. Greater bodily symmetry is linked to both higher cognitive test scores and faster RTs. It is possible, then, that differences in bodily system integrity indexed by symmetry may underlie the associations of RT and intelligence with increased longevity. However, RT and symmetry have seldom been examined in the same study, and never in children. Here, in 2 large samples aged 4 to 15 (combined n = 856), we found that more symmetrical children had significantly faster mean choice RT and less variability in RT. These associations of faster and less variable RT with greater symmetry early in life raise the possibility that the determinants of longevity in part originate in processes influencing bodily system integrity early in the life-course.

Objective:To determine the impact of cognitive interference on foot pedal reaction time among stroke survivors with right- (RH) or left-hemiplegia (LH).Design:Cross-sectional comparison without randomization.Subjects/patients:10 patients post-stroke with RH, 10 with LH; 10 age-matched controls.Methods:Foot pedal response times were measured using three different reaction time (RT) paradigms: simple RT, dual-task RT (counting backward by serial 3 seconds), and choice RT (correct response contingent on stimuli to eliminate pre-programing). RH and LH used the non-paretic leg for all trials. Three 3 (RT task) × 3 (group) mixed-model factorial ANOVAs were used to compare RT, movement time (MT), total response time (TRT).Results:Overall controls demonstrated faster RT than RH (332 ± 73 versus 474 ± 144 ms, P < 0.001) or LH (402 ± 127 ms, P < 0.05); LH group demonstrated faster RT than those with RH (P < 0.05). Control subjects demonstrated significantly faster RT than RH for all RT conditions (P < 0.05 for all). In contrast, controls achieved significantly faster RT than LH for the choice RT condition only (P < 0.05), but not for the simple (P = 0.12) or dual-task RT conditions (P = 0.25).Conclusions:Compared to controls, response time was significantly impaired among LH and RH when the response could not be pre-programmed. While current simple RT testing commonly employed by driver rehab specialists may be sufficient for detecting RT deficits in patients with RH, simple or dual-task RT tests alone may fail to detect RT deficiencies among LH, even when testing the non-paretic limb. Choice RT should be added to post-stroke driver fitness assessment, particularly for patients with LH.

Monkey Area MT Latencies to Speed Changes Depend on Attention and Correlate with Behavioral Reaction Times

Cortical Networks Implicated in Semantic and Episodic Memory: Common or Unique?

The objectives of this series of 3 studies were (a) to evaluate whether French-speaking children mainly use phonological mediation in the first stage of reading acquisition in a silent-reading task and (b) to examine the role of phonological processing in the construction of the orthographic lexicon. Forty-eight French children were followed from kindergarten to the end of Grade 2. Their phonological skills were assessed using a semantic categorization task with homophone and visual foils (Study 1); their orthographic skills were assessed using a choice task involving a correct exemplar, a homophone, and a visual foil (Study 2). In the semantic categorization task, the differences between the visual and homophone foils increased with time, as the homophone foils were more and more likely to be chosen. In the orthographic choice task, performance improved with time, but errors were more likely to involve homophone foils. The results obtained by two subgroups of children who differed in their level of orthographic expertise at the end of Grade 2 (Study 3) indicated that, 1 year earlier (at the end of Grade I), the future "expert" spellers were more likely than the future "poor" spellers to use phonological processing in silent reading (semantic categorization task). Moreover, in Grade 1, future expert spellers' phonological skills in reading aloud and in spelling from dictation (pseudoword tasks) were better than those of future poor spellers, and future expert spellers also had better phonological awareness skills at the beginning of the last year of kindergarten. These results suggest that French-speaking children use phonological mediation in silent-reading tasks and that phonological processing contributes to the construction of the orthographic lexicon.

Objective. Tetraplegic patients using brain–machine interfaces can make visually guided reaches with robotic arms. However, restoring proprioceptive feedback to these patients will be critical, as evidenced by the movement deficit in patients with proprioceptive loss. Proprioception is critical in large part because it provides faster feedback than vision. Intracortical microstimulation (ICMS) is a promising approach, but the ICMS-evoked reaction time (RT) is typically slower than that to natural proprioceptive and often even visual cues, implying that ICMS feedback may not be fast enough to guide movement. Approach. For most sensory modalities, RT decreases with increased stimulus intensity. Thus, it may be that stimulation intensities beyond what has previously been used will result in faster RTs. To test this, we compared the RT to ICMS applied through multi-electrode arrays in area 2 of somatosensory cortex to that of mechanical and visual cues. Main results. We found that the RT to single-electrode ICMS decreased with increased current, frequency, and train length. For 100 µA, 330 Hz stimulation, the highest single-electrode intensity we tested routinely, most electrodes resulted in RTs slower than the mechanical cue but slightly faster than the visual cue. While increasing the current beyond 100 µA resulted in faster RTs, sustained stimulation at this level may damage tissue. Alternatively, by stimulating through multiple electrodes (mICMS), a large amount of current can be injected while keeping that through each electrode at a safe level. We found that stimulation with at least 480 µA equally distributed over 16 electrodes could produce RTs as much as 20 ms faster than the mechanical cue, roughly the conduction delay to cortex from the periphery. Significance. These results suggest that mICMS may provide a means to supply rapid, movement-related feedback. Future neuroprosthetics may need spatiotemporally patterned mICMS to convey useful somatosensory information.Novelty & SignificanceIntracortical microstimulation (ICMS) is a promising approach for providing artificial somatosensation to patients with spinal cord injury or limb amputation, but in prior experiments, subjects have been unable to respond as quickly to it as to natural cues. We have investigated the use of multi-electrode stimulation (mICMS) and discovered that it can produce reaction times as fast or faster even than natural mechanical cues. Although our stimulus trains were not modulated in time, this result opens the door to more complex spatiotemporal patterns of mICMS that might be used to rapidly write in complex somatosensory information to the CNS.

Speed of information processing in the subacute stage after stroke was studied in 88 first ever, unilateral, ischemic stroke patients. The patient group included 42 right and 46 left hemisphere patients. Seventy-one control subjects were also examined. Four reaction time tasks with different levels of complexity were used: two visuomotor, and two semantic categorisation tasks. The results showed that stroke causes a decrease in decision making speed, but that the effect is different for right and left hemisphere patients. The right hemisphere group were slower than the control group on all reaction time tasks, and slower than the left hemisphere patients on the visuomotor tasks. The left hemisphere patients were slower than the healthy controls, only on the most complex tasks, the categorisation tasks.

Dissociated language functions are largely invalidated by standard techniques such as the amobarbital test and cortical stimulation. Language studies in which magnetoencephalography (MEG) and functional magnetic resonance (fMR) imaging are used to record data while the patient performs lexicosemantic tasks have enabled researchers to perform independent brain mapping for temporal and frontal language functions (MEG is used for temporal and fMR imaging for frontal functions). In this case report, the authors describe a right-handed patient in whom a right-sided insular glioma was diagnosed. The patient had a right-lateralized receptive language area, but expressive language function was identified in the left hemisphere on fMR imaging- and MEG-based mapping. Examinations were performed in 20 right-handed patients with low-grade gliomas (control group) for careful comparison with and interpretation of this patient's results. In these tests, all patients were asked to generate verbs related to acoustically presented nouns (verb generation) for fMR imaging, and to categorize as abstract or concrete a set of visually presented words consisting of three Japanese letters for fMR imaging and MEG. The most prominent display of fMR imaging activation by the verb-generation task was observed in the left inferior and middle frontal gyri in all participants, including the patient presented here. Estimated dipoles identified with the abstract/concrete categorization task were concentrated in the superior temporal and supramarginal gyri in the left hemisphere in all control patients. In this patient, however, the right superior temporal region demonstrated significantly stronger activations on MEG and fMR imaging with the abstract/concrete categorization task. Suspected dissociation of the language functions was successfully mapped with these two imaging modalities and was validated by the modified amobarbital test and the postoperative neurological status. The authors describe detailed functional profiles obtained in this patient and review the cases of four previously described patients in whom dissociated language functions were found.

Objective: The purpose of this study was to find out whether the simple reaction time was faster for auditory or visual stimulus and the factors responsible for improving the performance of the athlete. Methodology: 14 subjects were as- signed randomly into groups consisting of 2 members. Both the members from each group performed both the visual and auditory tests. The tests were taken from the DirectRT software program from a laptop. The DirectRT software consists of Testlabvisual and Testlabsounds to test the reaction times to visual and auditory stimuli. The 2 members from each group completed both the visual and auditory reaction times, the data was taken and the mean reaction time was calculated excluding the first and last values. Results: The results show that the mean visual reaction time is around 331 milliseconds as compared to the mean auditory reaction time of around 284 milliseconds. Conclusion: This shows that the auditory reaction time is faster than the visual reaction time. And also males have faster reaction times when compared to females for both auditory as well as visual stimuli.

This study examined the effects of systemic amphetamine in rats performing a reaction time task in which motivation and motor readiness were independently varied. Visual cues indicated the number of trials (one, two or three) needed before reinforcement was made available (i.e., reward cost). Lower reward cost was reflected in both a greater proportion of correctly completed trials and faster reaction times. Reaction times were also shorter as a function of increasing time from start of trial to the onset of the imperative stimulus (foreperiod), reflecting motor readiness or temporal probability summation. It was found that increasing dose of amphetamine resulted in faster reaction times, but the manner in which reaction time was speeded more closely resembled that of motor readiness than it did the speeding due to increasing motivation. Furthermore, the effects on performance of amphetamine and motivational condition were found to be entirely independent: there was no evidence to suggest that amphetamine enhanced, or disrupted, the expectation of forthcoming work or the response vigor which this engenders. It is concluded that systemic amphetamine does not act simply to amplify a natural reward signal. By contrast, amphetamine was found to enhance the effect of foreperiod, suggestive of a mechanism for the psychomotor stimulating effects of amphetamine.