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PubMed2001

Memory-enhancing effects of DHEAS in aged mice on a win-shift water escape task.

The steroid hormone, dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) have been implicated in age-associated deficits in memory. Numerous studies have demonstrated the effectiveness of these neurosteroids to enhance retention and ameliorate the effects of various memory-blocking agents, but few studies have directly assayed their effects on memory in aged animals. The present study investigated the memory-enhancing effects of DHEAS in a win-shift (nonmatching-to-sample) task in aged mice using water escape motivation. Sixteen CD-1 mice, 18-20 months old, were trained to a moderate criterion of 7/10 correct trials and were then divided into two equal groups based on acquisition performance. One group received oral administration of DHEAS (1.5 mg/mouse/day) in a vehicle solution (0.0015% methyl salicylate) while the other group received the vehicle alone. DHEAS effects were assessed using a procedure in which delay intervals (0, 120, and 240 s) were interposed between sample and comparison trials over the course of three test sessions. The group receiving DHEAS recorded significantly higher retention scores across 3 days of testing, particularly at the 120-s delay interval, indicating that DHEAS enhanced working memory in these aged animals.

Aging↗
PubMed1996

Effects of stimulus duration and task experience on gaze shift.

The effects of stimulus duration and prior task experience on gaze shift were studied to determine the spatial characteristics of gaze shift as affected by prior experience. Thirty-six subjects (with normal or corrected-to-normal vision) participated in two sessions of a task that required viewing two consecutively presented letters at either 15 degrees or 50 degrees eccentricity and deciding whether they were the same or different. In the first session (SS1) a letter was presented for either 500 (N = 18) or 1000 ms (N = 18), followed by a second letter. In session 2 (SS2), the groups were divided with half of the group performing the task under the same conditions as they did in SS1, while the other half was switched to the other first letter duration. Head and eye movements were recorded using a photoelectric transducer and electrooculogram (EOG), respectively. Few head movements occurred with targets presented at 15 degrees eccentricity. Approximately 80% of gaze shifts to the 50 degrees stimuli included a head movement component. DURATION had a significant effect on gaze shift. Head movement amplitude (HMA) increased, while saccade amplitude decreased with an increase in DURATION. On the average, the proportion of gaze shift accomplished via head movement was 24% if DURATION was 500 ms, and 37% when DURATION was extended to 1000 ms. SS1 task experience affected HMA in SS2. When DURATIONs differed between SS1 and SS2, HMA in SS2 were drawn toward the level of HMA in SS1. A positive and significant correlation was observed between head movement amplitude and head movement duration. The results suggest that both stimulus availability and prior experience affect head movement amplitude in gaze shift.

Adolescent↗
PubMed2004

Do children with focal cerebellar lesions show deficits in shifting attention?

More recent findings suggest a possible role of the cerebellum in nonmotor functions. Disability of individuals with cerebellar damage in rapidly shifting attention is one frequently used example to support cerebellar involvement in mental skills. The original proposal was based on findings in five children with chronic surgical lesions of the cerebellum and a young adult with a degenerative disorder. The aim of the present study was to repeat Akshoomoff and Courchesne's initial findings in a larger group of children with focal cerebellar lesions. Ten children with cerebellar lesions and 10 age- and sex-matched controls were tested. Neocerebellar areas were affected in all children with cerebellar damage except one based on detailed analysis of MRI scans. Subjects had to perform a focus and a shift attention task. Two visual and two auditory stimuli were presented in a pseudorandom order. An ellipse and a high-pitched tone were presented less frequently than a circle and a low-pitched tone. Rare stimuli were presented at five different time intervals. In the focus tasks, subjects had to react to the same rare stimulus of one of the two modalities. In the shift task, subjects had to switch between the two rare stimuli. Motor deficits based on reaction times were small in cerebellar children compared with controls. The ability of target detection did not significantly differ in the children with cerebellar lesions compared with the control children in both the focus and the shift attention task. In particular, children with cerebellar damage showed no significant impairment in rapid (<2 s) shifts of attention. The present findings indicate that the cerebellum may be less critical in attention related processes than suggested previously.

Adolescent↗
PubMed1997

Gaze-shift dynamics in two kinds of sequential looking tasks.

Gaze-shift dynamics of unrestrained seated subjects were examined. The subjects participated in two tasks. In the first task, they tapped sequences of 3-D targets located on a table in front of them. In the second task, they only looked at similar sequences of targets. The purpose of the task (tapping vs only looking) affected the dynamics of gaze-shifts. Gaze and eye-in-head peak velocities were higher and gaze-shift durations were shorter during tapping than during looking-only. We conclude that task variables affect gaze-shift dynamics, altering characteristics of the so-called saccadic "main sequence".

Fixation, Ocular↗
PubMed2005

Aging and inhibitory errors on a motor shift of set task.

Inhibitory functions are key mechanisms underlying age-related cognitive decline (Park and Gutchess in Cognitive aging: a primer, Psychology Press, Hove 2000), yet how these influence the control of action has not been fully investigated. Using 134 older (age 60-88) and 133 younger adults (age 20-59), we investigated in a motor analogy of the WCST the inhibition of a primed movement plan in favour of a novel one. Although 10% of older adults performed similarly to young adults, the majority failed to inhibit by the sixties, 10-20 years earlier than documented for the WCST (Lezak in Neurological Assessment, Oxford University Press, New York 1995; Haaland et al. in J Gerontol 33:345-346 1987). Around 40% failed to learn on the second attempt, and of these, the majority in their sixties to eighties failed to learn eventually. Implications are discussed for neuropsychological theory and everyday interventions.

Adult↗
PubMed1983

Reversal and nonreversal shifts in autistic children.

Reversal and nonreversal shifts in nineteen 2- to 14-year-old autistic children were studied. Each child was taught both a reversal and nonreversal shift discrimination task. The reversal shift condition entailed teaching the child to respond to one (the S+) of a pair of stimuli during training and subsequently reversing the S+ during testing. The nonreversal shift condition consisted of teaching the child two unrelated discriminations during training and testing. The results indicated that the older autistic children did better on reversal shifts than younger children who did better on nonreversal shifts. These findings are consistent with those for normal children.

Adolescent↗
PubMed2003

Assembling a task space: global determination of local shift costs.

Most theorizing on the origin of the costs that are associated with task shifts focuses on local transitions between individual trials. In the present article we argue that this emphasis has resulted in a neglect of more global representational structures, which also determinate shift costs. To substantiate this claim, we employed a set of four tasks that results from a factorial combination of two types of judgment and two judgment-to-response mappings. From previous work it is known that this kind of task combination is associated with a characteristic profile of shift costs as a function of the relation between successive tasks. Previously we have interpreted this profile as an indication of a hierarchically ordered dimensional representation of the two types of judgment and the two judgment-to-response mappings. Such a representation can only be expected to emerge when the two task features, judgment and mapping, vary independently of each other within the same situation. It is shown that the characteristic shift cost profile can indeed only be observed when the performance of any of the four tasks is required in a block of trials. In contrast, with only two tasks occurring in each block of trials, shift costs do not reflect the relation between successive tasks. This finding confirms the importance of global representational structures as a determinant of shift costs beyond local transitions between individual trials.

Adolescent↗
PubMed1996

A task analysis of the shift from teacher instructions to self-instructions in performing an in-common task.

Three preschool children repeatedly did four kinds of sorts with a deck of stimulus cards: a difficult, untaught target sort and three other sorts considered analytic of self-instructing the target performance. The untaught target sort was to find in a deck of cards those matching what two sample cards had in common. Most preschool children must be taught to mediate this problem. The three other kinds of sorts taught skills involved in the target performance or its mediation. As correct self-instructive talk emerged in the target sorts, it was confirmed. The untaught target sorts were interspersed infrequently among the three alternating directly taught skill sorts, to see if accurate target sorts, and accurate self-instructive talk about the target sorts, would emerge as the three skill sorts were mastered. As all the sorts progressed, increasing accuracy was seen first in the skill sorts and then in the untaught target sorts. All three subjects showed subsequent generalization to new target sorts involving other stimulus sets. Correct spontaneous self-instructions about the target sorts increased from near zero at the beginning of the experiment to consistency at its end. Thus the three skill sorts appeared sufficient for the emergence of a self-instructed solution to the previously insoluble target performance.

Child, Preschool↗
PubMed1998

Responses to irrelevant probes during task-induced negative and positive shifts.

The functional significance of task-induced negative and positive cortical shifts were tested with the probe-stimulus method. Both shifts were induced within the same experimental situation in three variants of a CNV paradigm, where a slow positive wave (a variant of P300) appeared following S2. In Experiment I and II, S2 called for making or withholding a motor response (go/no-go); in Experiment III, S2 informed the subject about the correctness of a previous guess. Irrelevant probe-stimuli were applied in conjunction with the task during the CNV, the post-S2 positivity and the intertrial interval (ITI). The probe-evoked vertex EPs were smaller during the post-S2 positivity as compared to the CNV and the ITI. This was true not only for the motor task but also for the guessing task, where the effect is unlikely to have been contaminated by motor potentials. This indicates that positive shifts have an inhibitory effect on the processing of irrelevant probe-stimuli and possibly on information-processing in general.

Adolescent↗
PubMed2006

Progressive increase of frontostriatal brain activation from childhood to adulthood during event-related tasks of cognitive control.

Higher cognitive inhibitory and attention functions have been shown to develop throughout adolescence, presumably concurrent with anatomical brain maturational changes. The relatively scarce developmental functional imaging literature on cognitive control, however, has been inconsistent with respect to the neurofunctional substrates of this cognitive development, finding either increased or decreased executive prefrontal function in the progression from childhood to adulthood. Such inconsistencies may be due to small subject numbers or confounds from age-related performance differences in block design functional MRI (fMRI). In this study, rapid, randomized, mixed-trial event-related fMRI was used to investigate developmental differences of the neural networks mediating a range of motor and cognitive inhibition functions in a sizeable number of adolescents and adults. Functional brain activation was compared between adolescents and adults during three different executive tasks measuring selective motor response inhibition (Go/no-go task), cognitive interference inhibition (Simon task), and attentional set shifting (Switch task). Adults compared with children showed increased brain activation in task-specific frontostriatal networks, including right orbital and mesial prefrontal cortex and caudate during the Go/no-go task, right mesial and inferior prefrontal cortex, parietal lobe, and putamen during the Switch task and left dorsolateral and inferior frontotemporoparietal regions and putamen during the Simon task. Whole-brain regression analyses with age across all subjects showed progressive age-related changes in similar and extended clusters of task-specific frontostriatal, frontotemporal, and frontoparietal networks. The findings suggest progressive maturation of task-specific frontostriatal and frontocortical networks for cognitive control functions in the transition from childhood to mid-adulthood.

Adolescent↗
PubMed2005

Shifts of effective connectivity within a language network during rhyming and spelling.

We used functional magnetic resonance imaging to examine task-specific modulations of effective connectivity within a left-hemisphere language network during spelling and rhyming judgments on visually presented words. We identified sites showing task-specific activations for rhyming in the lateral temporal cortex (LTC) and for spelling in the intraparietal sulcus (IPS). The inferior frontal gyrus (IFG) and fusiform gyrus were engaged by both tasks. Dynamic causal modeling showed that each task preferentially strengthened modulatory influences converging on its task-specific site (LTC for rhyming, IPS for spelling). These remarkably selective and symmetrical findings demonstrate that the nature of the behavioral task dynamically shifts the locus of integration (or convergence) to the network component specialized for that task. Furthermore, they suggest that the role of the task-selective areas is to provide a differential synthesis of incoming information rather than providing differential control signals influencing the activity of other network components. Our findings also showed that switching tasks led to changes in the target area influenced by the IFG, suggesting that the IFG may play a pivotal role in setting the cognitive context for each task. We propose that task-dependent shifts in effective connectivity are likely to be mediated through top-down modulations from the IFG to the task-selective regions in a way that differentially enhances their sensitivity to incoming word-form information.

Adult↗
PubMed2007

Temporal order is coded temporally in the brain: early event-related potential latency shifts underlying prior entry in a cross-modal temporal order judgment task.

The speeding-up of neural processing associated with attended events (i.e., the prior-entry effect) has long been proposed as a viable mechanism by which attention can prioritize our perception and action. In the brain, this has been thought to be regulated through a sensory gating mechanism, increasing the amplitudes of early evoked potentials while leaving their latencies unaffected. However, the majority of previous research has emphasized speeded responding and has failed to emphasize fine temporal discrimination, thereby potentially lacking the sensitivity to reveal putative modulations in the timing of neural processing. In the present study, we used a cross-modal temporal order judgment task while shifting attention between the visual and tactile modalities to investigate the mechanisms underlying selective attention electrophysiologically. Our results indicate that attention can indeed speed up neural processes during visual perception, thereby providing the first electrophysiological support for the existence of prior entry.

Adolescent↗
PubMed2000

Changing internal constraints on action: the role of backward inhibition.

Flexible control of action requires the ability to disengage from previous goals or task sets. The authors tested the hypothesis that disengagement during intentional shifts between task sets is accompanied by inhibition of the previous task set ("backward inhibition"). As an expression of backward inhibition the authors predicted increased response times when shifting to a task set that had to be abandoned recently and, thus, suffers residual inhibition. The critical backward inhibition effect on the level of abstractly defined perceptual task sets was obtained across 6 different experiments. In addition, it was shown that backward inhibition can be differentiated from negative priming (Experiment 2), that it is tied to top-down sequential control (Experiment 3), that it can account at least partially for "residual shift costs" in set-shifting experiments (Experiment 4), and that it occurs even in the context of preplanned sequences of task sets (Experiment 5).

Adult↗
PubMed2003

The role of attentional processes in children's prosocial behavior with peers: attention shifting and emotion.

This study evaluated the role of attentional shifting in children's prosocial behavior with peers. Participants were 27 aggressive/rejected and 27 nonaggressive/popular kindergarten and first grade boys and girls. Children's ability to shift attention from one affective state to another was assessed during: (a) a computerized task that required shifting attention between different affective events (i.e., the Children's Attentional Shifting Task, CAST) and (b) an analogue entry task with unacquainted peers. Children's latency for sharing with peers was assessed after they experienced failure during the entry task. Aggressive/rejected children had significant difficulty shifting attention from negative to positive affect during the CAST and were slower to share after experiencing entry failure. In general, aggressive/rejected children were less able to regulate their behavior effectively after experiencing social failure. Girls, regardless of status, had less difficulty than boys shifting attention from one affective state to another during the CAST. In addition, children's social status/aggressiveness, their ability to regulate emotional behavior after social failure and to shift attention effectively on the CAST predicted approximately 31% of the variance in their latency to share. These findings suggest that the ability to shift attention between different affective states plays a significant role in children's prosocial behavior with peers.

Affect↗
PubMed1994

Marmoset (Callithrix jacchus jacchus) spatial memory in a foraging task: win-stay versus win-shift strategies.

The spatial memory of common marmosets (Callithrix jacchus jacchus) was explored in 3 experiments with a simulated foraging task. In Experiment 1, individual monkeys foraged among 8 baited food sites. They appeared to use spatial memory to accurately avoid revisiting previously depleted sites. There was no difference in accuracy between the adult monkeys and a juvenile monkey tested on the same task. In Experiment 2, a win-stay paradigm was used. The adult monkey subject very accurately remembered locations that had previously contained food. The monkey tended to visit adjacent correct sites when retrieving food and thus minimized the total distance travelled. In Experiment 3, a win-shift paradigm was used with 2 adult monkeys. Although both monkeys performed at above-chance levels of accuracy on the win-shift task, they made many errors. These results suggest that marmosets may prefer tasks that require a win-stay strategy.

Animals↗
PubMed1999

Human eye-head gaze shifts in a distractor task. II. Reduced threshold for initiation of early head movements.

This study was motivated by the observation of early head movements (EHMs) occasionally generated before gaze shifts. Human subjects were presented with a visual or auditory target, along with an accompanying stimulus of the other modality, that either appeared at the same location as the target (enhancer condition) or at the diametrically opposite location (distractor condition). Gaze shifts generated to the target in the distractor condition sometimes were preceded by EHMs directed either to the side of the target (correct EHMs) or the side of the distractor (incorrect EHMs). During EHMs, the eyes performed compensatory eye movements to keep gaze stable. Incorrect EHMs were usually between 1 and 5 degrees in amplitude and reached peak velocities generally <50 degrees /s. These metrics increased for more eccentric distractors. The dynamics of incorrect EHMs initially followed a trajectory typical of much larger head movements. These results suggest that incorrect EHMs are head movements that initially were planned to orient to the peripheral distractor. Furthermore gaze shifts preceded by incorrect EHMs had longer reaction latencies than gaze shifts not preceded by incorrect EHMs, suggesting that the processes leading to incorrect EHMs also serve to delay gaze-shift initiation. These results demonstrate a form of distraction analogous to the incorrect gaze shifts (IGSs) described in the previous paper and suggest that a motor program encoding a gaze shift to a distractor is capable of initiating either an IGS or an incorrect EHM. A neural program not strong enough to initiate an IGS nevertheless can initiate an incorrect EHM.

Attention↗