Short-duration judgment in young Indian subjects under 30 h constant wakefulness.

The present study aimed to investigate probability of a possible endogenous circadian rhythm in human cognitive attribute to estimate short intervals. Apparently healthy young males and females were selected for our study. Eight subjects prospectively produced the short-time intervals 10 s and 60 s at 2 hourly intervals in 30 h constant routine (CR) study conducted in spring (CR-1). The study was repeated again in autumn (CR-2) in the remaining eight subjects. The established circadian markers, namely serum cortisol, salivary melatonin levels and tympanic temperature were also measured either in CR-1 or CR-2. Oral temperature was measured simultaneously. Circadian rhythms were validated in serum cortisol, salivary melatonin, oral, and tympanic temperatures. Circadian rhythm in 60 s estimates was observed in a few subjects and in all males at group level in CR-1. The cognitive attribute to perceive short intervals vary as function of season. The results provide evidence in support of interaction among the interval, circadian and circannual timing systems in human.

Advanced Circadian Timing and Sleep Fragmentation Differentially Impact on Memory Complaint Subtype in Subjective Cognitive Decline.

BACKGROUND: Increased sleep fragmentation and advanced circadian timing are hallmark phenotypes associated with increased age-related cognitive decline. Subjective cognitive decline (SCD) is considered a prodromal stage of neurodegeneration and dementia; however, little is known about how sleep and circadian timing impact on memory complaints in SCD. OBJECTIVE: To determine how sleep and circadian timing impact on memory complaint subtypes in older adults with SCD. METHODS: Twenty-five older adults with SCD (mean age = 69.97, SD = 5.33) completed the Memory Functioning Questionnaire to characterize their memory complaints. They also underwent neuropsychological assessment, and completed 1 week of at-home monitoring of sleep with actigraphy and sleep diaries. This was followed by a two-night laboratory visit with overnight polysomnography and a dim light melatonin onset assessment to measure circadian timing. RESULTS: Advanced circadian timing was associated with greater memory complaints, specifically poorer memory of past events (r = -0.688, p = 0.002), greater perceived decline over time (r = -0.568, p = 0.022), and increased reliance on mnemonic tools (r = -0.657, p = 0.004). Increased sleep fragmentation was associated with reduced self-reported memory decline (r = 0.529, p = 0.014), and reduced concern about everyday forgetfulness (r = 0.435, p = 0.038). CONCLUSION: Advanced circadian timing was associated with a number of subjective memory complaints and symptoms. By contrast, sleep fragmentation was linked to lowered perceptions of cognitive decline, and less concern about memory failures. As circadian disruption is apparent in both MCI and Alzheimer's disease, and plays a key role in cognitive function, our findings further support a circadian intervention as a potential therapeutic tool for cognitive decline.

Effect of clozapine on interval timing and working memory for time in the peak-interval procedure with gaps.

Previous research indicates that dopamine controls both the speed of an internal clock [Maricq, A.V., Church, R.M., 1983. The differential effects of haloperidol and methamphetamine on time estimation in the rat. Psychopharmacology 79, 10-15] and sharing of resources between the timer and other cognitive processes [Buhusi, C.V., 2003. Dopaminergic mechanisms of interval timing and attention. In: Meck, W.H. (Ed.), Functional and Neural Mechanisms of Interval Timing. CRC Press, Boca Raton, FL, pp. 317-338]. For example, dopamine agonist methamphetamine increases the speed of an internal clock and resets timing after a gap, while dopamine antagonist haloperidol decreases the speed of an internal clock and stops timing during a gap [Buhusi, C.V., Meck, W.H., 2002. Differential effects of methamphetamine and haloperidol on the control of an internal clock. Behav. Neurosci. 116, 291-297]. Using a 20-s peak-interval procedure with gaps we examined the acute effects of clozapine (2.0mg/kg i.p.), which exerts differential effects on dopamine and serotonin in the cortex and striatum, two brain areas involved in interval timing and working memory. Relative to saline, clozapine injections shifted the response functions leftward both in trials with and without gaps, suggesting that clozapine increased the speed of an internal clock and facilitated the maintenance of the pre-gap interval in working memory. These results suggest that clozapine exerts effects in different brain areas in a manner that allows for the pharmacological separation of clock speed and working memory as a function of peak trials without and with gaps.

Hypothesis concerning embodied calendars: A case study of number form, color spreading, and taste-color synaesthesia.

We propose a hypothesis concerning the neural basis of the mental 'calendar' we all carry around in our brains, based on observations we made on a 25year old 'projector synaesthete', EA, who displays some novel and instructive features. In addition to her grapheme-color synaesthesia, she has a circular 'calendar line', laid out vividly in front of her in the horizontal plane with December 31st passing through the middle of her chest and other months arranged in clockwise sequence ending with December on her right (July was 3 feet in front of her). Her access to episodic memories felt, subjectively, as if it was facilitated by her calendar line. Intriguingly, if she turned her sideways to look to the right, the calendar remained 'stuck to the chest' - meaning that it was body centered rather than head centered. Even more surprising is how, when she rotated her head rightward, the left portion of her calendar became "fuzzy", and memories of February and March became less accessible; a striking example of embodied cognition - memories gated by information from neural networks representing the activity of neck muscles. We postulate that the human calendar is mediated by connections between the angular gyrus and hippocampal place and time cells-via the inferior longitudinal fasciculus. Other aspects of EA's synaesthesia were also explored. The colors evoked by graphemes spread outside the grapheme itself, but the spread could be blocked by real as well as illusory contours. These interactions might be mediated by cells signaling illusory contours (in V2) and color/texture sensitive cells in (V4). Tastes also evoked colors, but, intriguingly, the colors were experienced inside her mouth rather than out there in the world. We discuss the deeper implications of these findings for understanding the nature of quale, and the manner in which the self anchors itself in space and time.

Sex hormones modulate neurophysiological correlates of visual temporal attention.

The functional cerebral asymmetry (FCA) in processing targets within rapid serial visual presentation (RSVP) streams has been reported to fluctuate across the menstrual cycle, with identification of the second of two closely spaced targets being impaired when both targets occur in the left or the right hemifield stream during the luteal phase, while during the menstrual phase identification of the second target is only impaired for target pairs presented in the right hemifield stream. This fluctuation has been proposed to result from variations in estradiol levels. The current study used EEG to investigated whether the cycle-related fluctuation in RSVP target identification FCA relates to changes in early, stimulus-driven, bottom-up or in later, top down-driven aspects of FCA. While the former would be expected to become evident in the early visual evoked potentials (VEPs) P1 or N1, the latter would be evident in later event-related potentials (ERPs) such as N2pc or P3. Women performed a dual-stream RSVP task once during the menstrual phase and once during the follicular phase. Estradiol levels were determined from saliva samples. In contrast to previous findings, FCA in RSVP target identification was not affected by cycle phase. However, the impairment in second-target identification when targets where closely spaced was generally smaller during the menstrual phase than during the follicular phase. This effect was matched by shorter peak latencies of P1 VEPs for the menstrual phase, and by a reduction in the latency of the second-target P3 ERP for closely spaced relative to widely spaced target pairs, again for the menstrual phase. Results suggest that in a dual-stream RSVP setup, target identification, early stage stimulus processing, and target consolidation are affected by cycle phase, but that the asymmetry of these effects does not differ between menstrual and follicular phase. The observed cycle-related modulations in neurophysiology and behavior could relate to the effects of estradiol on the locus ceruleus norepinephrine (LC-NE) system, which is known to play a major role in arousal, attention and stress response.

No morning cortisol response in patients with severe global amnesia.

Activity of the hypothalamus pituitary adrenal (HPA) axis is characterized by a pronounced circadian rhythm. An acute increase in cortisol levels occurs after awakening in the morning with continuously declining levels over the course of the remaining day. The morning cortisol increase probably reflects an activational response of the HPA axis aimed at preparing the body for the day. Some studies found patterns of enhanced or blunted waking cortisol responses observed under chronic stress, burnout, or post traumatic stress disorder. The present study wanted to characterize the morning cortisol response and the circadian cortisol day profile in a sample of six male patients with severe amnesia due to hypoxia, herpes simplex encephalitis or closed head injury. Age and gender matched relatives or friends served as controls. Cortisol was measured from saliva samples collected at home on two consecutive days. The patients were woken up in the morning by their partners or caregivers. The morning cortisol increase typically observed in healthy subjects and also observed in the control group was absent in the amnesic patients. In contrast, a normal circadian day profile was found in the amnesic patients, with a pronounced circadian cortisol decrease. Further studies are needed to understand the neurological or psychological mechanisms leading to a missing morning cortisol response in amnesic patients.

A time to be stressed? Time perspectives and cortisol dynamics among healthy adults.

Perceptions of past, present, and future events may be related to stress pathophysiology. We assessed whether Time Perspective (TP) is associated with cortisol dynamics among healthy adults (N=61, Ages=18-35, M=22.9, SD=4.1) exposed to the Trier Social Stress Test (TSST). TP was measured according to two profiles: maladaptive Deviation from Balanced TP (DBTP) and adaptive Deviation from Negative TP (DNTP). Eight salivary cortisol samples were analyzed using area under the curve with respect to ground (AUCg) and to increase (AUCi). Statistic analyses involved partial correlations controlling for depressive symptoms. Results for both sexes showed that higher DBTP scores were associated with lower cortisol AUCg scores, while higher DNTP scores were associated with higher cortisol AUCg scores. These novel findings suggest that maladaptive TP profiles influence hypocortisolism, whereas adaptive TP profiles influence hypercortisolism. Thus, TP profiles may impact conditions characterized by altered cortisol concentrations.

Neural systems supporting timing and chronometric counting: an FMRI study.

At least two strategies are available to humans for estimating multisecond intervals. One depends on an interval timing system that is common to many species. The other is the language-based strategy of chronometric counting. These two strategies are easily distinguished by the psychophysical properties of their behavioral correlates: counting supports substantially more precise estimates than are possible using the more general interval timing system. The present study investigates the neural systems that underlie the execution of these different strategies. Eighteen adults reproduced a 16-s interval either by internally timing or covertly counting the duration. Comparison of counting and timing to a resting baseline suggested that these strategies engage some nonoverlapping neural systems. Counting, but not timing, strongly activated Broca's area, primary motor cortex in the mouth region, and right cerebellum, all of which are associated with internal speech. Counting also activated parts of the medial premotor circuit, including the putamen, supplementary motor area (SMA) proper, and cingulate motor area (CMA), that have been associated with reproducing isochronous and syncopated rhythms of elements lasting hundreds of milliseconds. During timing, only a portion of this circuit, the SMA proper and CMA, was engaged. Both timing and counting interfered with semantic processing during the resting state, evidenced by task-related decreases in the left inferior and middle frontal gyri, right superior frontal gyrus, left angular gyrus, and bilateral posterior cingulate cortex. This study suggests that counting activates a corticostriatal network associated with millisecond, rhythmic timing. In contrast, timing long durations without the benefit of linguistic strategies for subdividing counts reduces activity in this circuitry.

Re-imagining motor imagery: building bridges between cognitive neuroscience and sport psychology.

One of the most remarkable capacities of the mind is its ability to simulate sensations, actions, and other types of experience. A mental simulation process that has attracted recent attention from cognitive neuroscientists and sport psychologists is motor imagery or the mental rehearsal of actions without engaging in the actual physical movements involved. Research on motor imagery is important in psychology because it provides an empirical window on consciousness and movement planning, rectifies a relative neglect of non-visual types of mental imagery, and has practical implications for skill learning and skilled performance in special populations (e.g., athletes, surgeons). Unfortunately, contemporary research on motor imagery is hampered by a variety of semantic, conceptual, and methodological issues that prevent cross-fertilization of ideas between cognitive neuroscience and sport psychology. In this paper, we review these issues, suggest how they can be resolved, and sketch some potentially fruitful new directions for inter-disciplinary research in motor imagery.

Diurnal fluctuations in subjective sleep time in humans.

Humans have the ability to estimate the passage of time in the absence of external time cues. In this study, we subjected 22 healthy males (aged 21.8±1.9 years) to a 40-min nap trial followed by 80min of wakefulness repeated over 28h, and investigated the relationship between various sleep parameters and the discrepancy (ΔST) of time estimation ability (TEA) during sleep, defined by the difference between actual sleep time (ST) and subjective sleep time (sub-ST) in each nap interval. Both ST and sub-ST were significant diurnal fluctuations with the peak in the early morning (9h after dim-light melatonin onset time, 2h after nadir time of core body temperature rhythm), and subjective sleep duration was estimated to be longer than actual times in all nap intervals (sub-ST>ST). There were significant diurnal fluctuations in discrepancy (sub-ST-ST) of TEA during sleep, and the degree of discrepancy correlated positively with increase in the amount of REM sleep and decrease in the amount of slow-wave sleep. These findings suggest that human TEA operates at a certain level of discrepancy during sleep, and that this discrepancy might be related to the biological clock and its associated sleep architecture.

Psychosocial stress attenuates general sound processing and duration change detection.

An EEG-compatible adaptation of the Trier Social Stress Test was developed to induce psychosocial stress in healthy subjects while investigating their auditory processing of unattended sounds and salivary levels of the stress hormone cortisol. The mismatch negativity (MMN) and N1/P2 were assessed using a multifeature paradigm, while subjects were attending to visual tasks with high or low attentional workload. Only the responses to duration change were affected by the stress manipulation. Cortisol levels during stress were inversely related to the MMN amplitudes of duration deviants. During anticipatory stress, responses to the standard tones (general sound processing) increased, but their amplitude was not correlated with cortisol levels. We found that psychosocial stressor anticipation attenuates both general and deviance-specific sound processing, suggesting that cortisol interferes with cortical memory-trace formation.

Spatial and temporal factors during processing of audiovisual speech: a PET study.

Speech perception can use not only auditory signals, but also visual information from seeing the speaker's mouth. The relative timing and relative location of auditory and visual inputs are both known to influence crossmodal integration psychologically, but previous imaging studies of audiovisual speech focused primarily on just temporal aspects. Here we used Positron Emission Tomography (PET) during audiovisual speech processing to study how temporal and spatial factors might jointly affect brain activations. In agreement with previous work, synchronous versus asynchronous audiovisual speech yielded increased activity in multisensory association areas (e.g., superior temporal sulcus [STS]), plus in some unimodal visual areas. Our orthogonal manipulation of relative stimulus position (auditory and visual stimuli presented at same location vs. opposite sides) and stimulus synchrony showed that (i) ventral occipital areas and superior temporal sulcus were unaffected by relative location; (ii) lateral and dorsal occipital areas were selectively activated for synchronous bimodal stimulation at the same external location; (iii) right inferior parietal lobule was activated for synchronous auditory and visual stimuli at different locations, that is, in the condition classically associated with the 'ventriloquism effect' (shift of perceived auditory position toward the visual location). Thus, different brain regions are involved in different aspects of audiovisual integration. While ventral areas appear more affected by audiovisual synchrony (which can influence speech identification), more dorsal areas appear to be associated with spatial multisensory interactions.