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PubMed2002

Movement-related neuronal activity reflecting the transformation of coordinates in the ventral premotor cortex of monkeys.

We examined how the transformation of coordinates from visual to motor space is reflected by neuronal activity in the ventral premotor cortex (PMv) of monkeys. Three monkeys were trained to reach with their right hand for a target that appeared on a screen. While performing the task, the monkeys wore prisms that shifted the image of the target 10 degrees, left or right, or wore no prisms, for a block of 200 trials. The nine targets were located in the same positions in visual space regardless of whether the prisms were present. Wearing the prisms required the monkeys to initiate a movement in a direction that was different from the apparent target location. Thus using the prisms, we could dissociate visual space from motor space. While the monkey performed the behavioral task, we recorded neuronal activity in the left PMv and primary motor cortex (MI), and various kinds of task-related neuronal activity were found in the motor areas. These included neurons that changed their activity during a reaction time (RT) period (the period between target presentation and movement onset), which were called "movement-related neurons" and selected for analysis. In these neurons, activity during a movement time (MT) period was also compared. Using general linear models for our statistical analysis, the neurons were then classified into four types: those whose activity was consistently dependent on location of targets in the visual coordinates regardless of whether the prisms were present or absent (V type); those that were consistently dependent on target location in the motor coordinates only; those that had different activity for both of the motor and visual coordinates; and those that had nondifferential activity for the two types of coordinates. The proportion of the four types of the neurons differed significantly between the PMv and MI. Most remarkably, neurons with V-type activity were almost exclusively recorded in the PMv and were almost exclusively found during the RT period. Such activity was never observed in an electromyogram of the working forelimb. Based on these observations, we postulate that the V and other types may represent the various intermediate stages of the transformation of coordinates and that the PMv plays a crucial role in transforming coordinates from visual to motor space.

Animals↗

PubMed2003

Muscle synergies during shifts of the center of pressure by standing persons: identification of muscle modes.

When a standing person performs a movement such that the center of gravity shifts, the activity of postural muscles adjusts to keep the balance. We assume that such adjustments are controlled using a small set of central variables, while each variable induces changes in the activity of a subgroup of postural muscles. The purpose of this study has been to identify such muscle groups (muscle modes or M-modes) and compare them across tasks and subjects. Four tasks required the subjects to release a load from extended arms leading to a center of pressure (COP) shift prior to the load release. The fifth task required an explicit COP shift by voluntary sway. Electromyographic activity of 11 postural muscles on one side of the body was integrated over a 100-ms interval corresponding to the early stage of the COP shift, and this integrated EMG activity was subjected to a principal component (PC) analysis across multiple repetitions of each task. Three PCs were identified and associated with a "push-back M-mode," a "push-forward M-mode," and a "mixed M-mode." Cluster analysis of the PC vectors across tasks and across subjects confirmed the existence of distinctive push-forward and push-back muscle groups. PC vectors were also compared across tasks and across subjects using cosines as a measure of colinearity between pairs of vectors. In general, M-modes were similar across both tasks and subjects. We conclude that shifts of the COP, whether implicit or explicit, are controlled using a small set of central variables associated with changes in the activity of robust subsets of postural muscles. These results can be used for future analysis of muscle synergies associated with postural tasks.

Adult↗

PubMed2000

Modulation of task-related neural activity in task-switching: an fMRI study.

Task-switching paradigms, in which subjects are typically asked to switch between different S-R mappings, can be considered operationalizations of executive control. Such paradigms are therefore potentially useful in investigating the neural bases of control functions. Here, we present the results of an fMRI study intended to examine two separable components of task-switching: preparation, and the residual shift cost identified by Rogers and Monsell [13]. In analyses restricted to functionally identified regions of interest, we found robust evidence of greater activity for switch trials, compared to repeat trials. This pattern was present both at the time of stimulus presentation and prior to the switch trial. In analyses of the entire brain, we were able to identify one area in the superior parietal lobule that was active during switching but was not part of the apparent network of task-related regions. We conclude that switch trials are neurally distinct from repeat trials in eliciting generally greater neural activity both before and during the performance of a trial.

Adult↗

PubMed1989

Progressive decline of picture naming in an aging Down syndrome man with dementia.

This study was conducted to monitor picture naming longitudinally in a 59-yr.-old Down syndrome man with diagnosed dementia. On the test, the subject was shown a series of 40 pictures, and his task was to speak their names. Correct naming responses were followed by pennies. The test was repeated periodically over the course of 20 mo. The subject initially achieved 100% correct scores and maintained accuracy until the tenth month. Thereafter, his scores declined, gradually at first and then precipitously, until the subject scored less than 30% correct on the final test. Error analysis showed that low scores generally reflected loss of stimulus control by relevant characteristics of the test pictures; control apparently shifted to irrelevant features of the task. The results suggest that naming tests may ultimately prove useful in defining and documenting the nature of deterioration in Down dementia.

Age Factors↗

PubMed1999

Mechanisms underlying attentional set-shifting in Parkinson's disease.

Patients with Parkinson's disease (PD) show impairments on tasks that require them to switch attention between two perceptual dimensions (extradimensional (ED) shifting). It has been suggested that ED shifting deficits can be caused by two separate mechanisms, 'learned irrelevance' and 'perseveration'. This study set out to test the hypothesis that enhanced learned irrelevance is present in medicated patients with PD. An enhancement of learned irrelevance in PD patients should result in increased errors on a 'deficit' shift relative to controls and decreased errors on an 'improvement' shift. A similar pair of deficit and improvement shifts were used to detect possible enhanced perseveration in patients. Instead of showing the predicted patterns of deficit and improvement, patients displayed a consistent deficit on those shifts that required that they switch their attention to a different dimension (ED shifts). In contrast, patients were not impaired on shifts that required no such shift of attention (intradimensional shifts). Although there was an increase in errors at the learned irrelevance deficit shift, a similar increase at the learned irrelevance improvement shift shows that enhanced learned irrelevance is not responsible for either of these results. Patients were no more distractible than controls, but displayed increased 'loss of set' as measured by errors generated after a rule was learned. These results point to the existence of exaggerated, rigid selective attention in patients with PD rather than a breakdown in the ability to selectively attend. There was no evidence for the existence of enhanced learned irrelevance in the patients.

Aged↗

PubMed1993

Changes in visuospatial attention over the adult lifespan.

Shifts of visual attention elicited by spatial cues were examined for detection and letter-discrimination tasks in 90 normal adults ranging in age over each decade from the 20s to the 70s. Spatial cues were valid, invalid, or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7 degrees to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200, 500 and 2000 msec. Reaction time (RT) costs and benefits associated with spatial cueing did not vary with age for: (1) the detection task; (2) the letter-discrimination task with peripheral cues; and (3) the letter-discrimination task with central cues at a short (200 msec) SOA. RT costs and benefits increased with age only for SOAs greater than 200 msec with central cueing in the discrimination task. In general, the efficiency of cue-based shifts of visuospatial attention appears relatively resistant to the effects of adult age up to 79 years. When an age effect was found, RT costs and benefits increased steadily across all age decades, the correlation with age being 0.25 and 0.38 for the 500 and 2000 msec SOAs, respectively. The findings suggest a qualitative difference in the influence of normal adult aging and effects of dementia noted in previous studies; normal aging has only a weak influence on voluntary attention shifts, whereas dementia affects both voluntary and involuntary modes of attention shifting.

Adult↗

PubMed1994

Attention shifts produce spatial stimulus codes.

In the Simon task the spatial position of the stimulus, though task irrelevant, influences speed of response. We (Umiltà & Nicoletti, 1992) proposed that the orienting of attention to the imperative stimulus produces a Stroop-like interference. This paper reports the results of three experiments that provide empirical support for two predictions of this hypothesis. One is that the stimulus spatial code is formed with relation to the position to which attention is directed. The other prediction is that the Simon effect is obtained on condition that attention can orient to the stimulus.

Adult↗

PubMed1996

Shifts in children's ear asymmetry during verbal and nonverbal auditory-visual association tasks: a "virtual stimulus" effect.

Dichotic consonant-vowel-consonant (CVC) syllables were presented to 96 right-handed children between the ages of 8 and 12 years. Children were assigned either to a "code" condition that entailed translating the CVCs into English words or to a "bird" condition in which the CVCs had to be matched to cartoons of birds. A differential ear asymmetry for the code and bird tasks developed linearly across four blocks of trials. By Block 4, the code task yielded a significant right-ear advantage and the bird task yielded no ear advantage. The results are inconsistent with any model that attributes ear asymmetries entirely to fixed structural characteristics of the nervous system. Instead, ear asymmetries are influenced by the subject's categorization of the stimuli, i.e., by "virtual stimuli". These appear to be constructed over time (blocks of trials).

Association Learning↗

PubMed1988

Left frontal lobe in verbal associative learning: a slow potential study.

In the present experiment pairs of words had to be memorized. The words were either meaningful or meaningless. The experimental design compares conditions of preestablished learning (L-) with active learning (L+). The effects of these two factors, "semantic content (S)" and "learning (L)", on the slow potential shifts accompanying presentation and processing of the verbal material were tested. In the memorizing tasks, the two words were given in a fixed temporal sequence. A slow negative potential shift having a maximum in parietal leads emerged within the inter-stimulus-interval. Its amplitudes were larger in the learning tasks (L+) than in conditions of pre-established learning (L-). This difference of amplitudes may reflect different levels of attention: In L-, the second word could be anticipated, but not in the L+ tasks. After the presentation of the second item, learning tasks (L+) were characterized by a slow negative potential shift in the recordings of the left dorso-lateral frontal lobe. It is assumed that this potential shift may indicate an importance of the left frontal lobe in the elaborative encoding of verbal material.

Adult↗

PubMed1988

Constraints on water maze spatial learning in rats: implications for behavioral studies of brain damage and recovery of function.

In an effort to develop spatial learning tasks not requiring food or water deprivation for use in studies of recovery of function after brain damage, T-maze spatial alternation learning was examined in intact rats using water maze swim-escape procedures. Consistent with previous studies, rewarded spatial alternation involving food or water deprivation was readily learned by intact rats. However, none of the groups of rats trained in the swim-escape tasks learned to alternate goal arm choices in the water maze at reliable rates. This was true regardless of whether non-correction or correction procedures were used, and regardless of intertrial delay intervals. Although average alternation rates over sessions did increase from chance levels, the majority of the rats did not reach criterion levels, even with as many as 38 consecutive days of testing. In contrast, a conditional spatial alternation task in the water maze, using a win-shift procedure, was readily learned. Surprisingly, a win-stay version of this conditional spatial task was not learned over 21 days of testing. These unexpected constraints on spatial learning and memory processes in rats cannot be attributed simply to failure of spatial information processing, nor to strict limitations on working memory in swim-escape tasks, since excellent spatial navigation abilities have been documented, and mastery of at least some working-memory tasks have now been demonstrated in swim-escape tasks.

Animals↗

PubMedDate not supplied

Mapping human visual cortex with positron emission tomography.

Positron-emission tomography (PET) can localize functions of the human brain by imaging regional cerebral blood flow (CBF) during voluntary behaviour. Functional brain mapping with PET, however, has been hindered by PET's poor spatial resolution (typically greater than 1 cm). We have developed an image-analysis strategy that can map functional zones not resolved by conventional PET images. Brain areas selectively activated by a behavioural task can be isolated by subtracting a paired control-state image from the task-state image, thereby removing areas not recruited by the task. When imaged in isolation the centre of an activated area can be located very precisely. This allows subtle shifts in response locale due to changes in task to be detected readily despite poor spatial resolution. As an initial application of this strategy we mapped the retinal projection topography of human primary visual cortex. Functional zones separated by less than 3 mm (centre-to-centre) were differentiated using PET CBF images with a spatial resolution of 18 mm. This technique is not limited to a particular brain area or type of behaviour but does require that the increase in CBF produced by the task be both intense and focal.

Cerebrovascular Circulation↗

PubMed2003

Endogenous shifts of covert attention operate within multiple coordinate frames: evidence from a feature-priming task.

The locations of visual objects and events in the world are represented in a number of different coordinate frameworks. For example, a visual transient is known to attract (exogenous) attention and facilitate performance within an egocentric framework. However, when attention is allocated voluntarily to a particular visual feature (ie endogenous attention), the location of that feature appears to be variously encoded either within an allocentric framework or in a spatially invariant manner. In three experiments we investigated the importance of location for the allocation of endogenous attention and whether egocentric and/or allocentric spatial frameworks are involved. Primes and targets were presented in four conditions designed to vary systematically their spatial relationships in egocentric and allocentric coordinates. A reliable effect of egocentric priming was found in all three experiments, which suggests that endogenous shifts of attention towards targets defined by a particular feature operate in an egocentric representation of visual space. In addition, allocentric priming was also found for targets primed by their colour or shape. This suggests that attending to targets primed by nonspatial attributes results in facilitation that is localised in more than one coordinate frame of spatial reference.

Analysis of Variance↗

PubMed1994

Age-related effects of the nicotinic antagonist mecamylamine on cognition and behavior.

Studies of the neurochemical pathology of Alzheimer's disease and Parkinson's disease reveal a severe and specific loss of central nicotinic cholinergic receptors. We have investigated the functional significance of this finding for cognitive functioning by studying the effects of the centrally active nicotinic antagonist mecamylamine. Single oral doses of mecamylamine were administered to 12 healthy young males and 15 healthy elderly subjects in doses of 5, 10, and 20 mg in a placebo-controlled, double-blind study. In both groups, the 20-mg dose caused a significant increase in errors in the learning condition of the Repeated Acquisition Task, producing a slower acquisition curve. There was no effect of drug on the performance component (retrieval of previously learned information). However, elderly subjects showed enhanced sensitivity to mecamylamine, with 10-mg dose producing significant impairment of learning not seen in the young normals. On a recognition memory task, there was an age-associated shift in response bias, with the elderly subjects becoming more liberal with increasing dose. Reaction-time measures suggested a dose-related slowing of reaction time on several tasks. Behavioral effects were minimal and physiologic effects were consistent with dose-related ganglionic blockade. These results indicate that acute blockade of nicotinic receptor function can produce measurable and significant cognitive impairment similar to some deficits seen in dementing illnesses, and that there is an age-related increase in sensitivity to nicotinic blockade.

Adult↗

PubMed1989

Parallel development of ethanol tolerance and operant compensatory behaviors in rats.

This experiment was designed to detect compensatory learning that has been suggested to occur during the course of tolerance development to ethanol's effects on operant performance. The effects of presession ethanol injections on the development of tolerance to ethanol's effects on operant performance in an afternoon Fixed-Ratio (FR) task was assessed in rats that were concurrently performing in a morning DRL task. Only presession saline injections were administered for the DRL task. A cumulative dosing procedure was used to establish initial and postethanol exposure dose-effect curves for both tasks. Daily presession ethanol administration produced a 3-fold shift-to-the-right in the dose-effect curve for FR-task performance. No changes were evident in the FR-task performance of controls that received daily saline injections. However, during the period of daily ethanol injections and during subsequent cumulative dose tests, the ethanol, but not the control, group displayed dose-related increases in total DRL-task responses relative to baseline. These DRL data were interpreted as reflecting the development of rate-increasing behaviors that compensated for and contributed to the tolerance of ethanol's rate-decreasing effects on FR-task performance.

Animals↗

PubMed2000

The dynamics of shifting visuospatial attention revealed by event-related potentials.

We developed a behavioral task for spatial orienting of attention in which the same physical stimulus cued covert peripheral shifts of attention to either the left or the right visual fields in different conditions. The design enabled us to record the brain activity engaged during spatial shifts of covert attention that was independent from the physical characteristics of the cueing stimulus using event-related potentials (ERPs). ERPs elicited by foveal cues differed according to the predicted target location starting ca. 160 ms, and differences persisted until the occurrence of the target stimuli. Multiple processes were linked to shifting spatial attention during the cue-target interval. The earliest effects consisted of enhanced negative potentials over the posterior scalp contralateral to the cued location. Later effects were concentrated over the right anterior scalp sites, where activity associated with shifts to the right visual field elicited larger positive potentials. The results extend our understanding of the neural system that orients spatial attention by providing valuable information about the temporal dynamics and hemispheric asymmetries of activity within its posterior and anterior regions.

Adult↗

PubMed1993

Information processing in children with minor neurological dysfunction: behavioural and neurophysiological indices.

Minor neurological dysfunction (MND) refers to deviant function of the central nervous system in the absence of localizable neurological disorders. Children with no signs (n = 28) and with varying grades of MND (n = 48), classified according to failure on circumscript neurological subsystems, were administered selective and sustained attention tasks at the age of twelve. During the execution of one of the tasks, electrocortical activity of the brain was recorded at the Fz, Cz, Pz and Oz scalp locations. Of main interest were behavioural and electrophysiological indices of deficits in attentional control. With respect to the latter category, the investigation was focused on differences in event-related potential amplitudes reflecting subprocesses of cognitive processing (processing negativity, P300). Following a linear stage model of information processing, it was found that children who failed on three or more neurological subsystems (in particular on fine manipulation and coordination), exhibited deficits in the encoding, search and decision stages of processing. Furthermore, the children with MND showed a reduced positive parietal shift on target presentation. Under complex task conditions, children without MND showed a decrease in P300 amplitude which reflects the impact of processing negativity as a result of increased task demands; this effect was absent in children with MND. These electrocortical differences suggest imbalances in the external and internal neural regulation of the flow of information in the brain.

Attention↗

PubMed2004

Passive enhancement of the somatosensory P100 and N140 in an active attention task using deviant alone condition.

OBJECTIVE: We investigated the changes in the somatosensory P100 and N140 during passive (reading) versus active tasks (counting, button pressing) and oddball (target=20%, standard=80%) versus deviant alone conditions (standards were omitted). METHODS: Nine healthy subjects performed the 3 tasks (reading, counting and button pressing) under two conditions. Standard and target electrical stimuli were presented in a random order to the index or middle fingers of the left hand at a constant 800 ms interstimulus interval in the oddball conditions. In the deviant alone conditions, only target stimuli were presented with the same timing as in the oddball conditions. RESULTS: The N140 amplitude increased for the deviant alone stimuli compared with the oddball standard and target stimuli regardless of whether the task was passive or active, indicating passive shifts of attention related to temporal infrequency. The P100 amplitude also increased for the deviant alone stimuli compared with the oddball standard and target stimuli in both passive and active tasks, but the enhancement seemed to be even smaller than that of the N140 amplitude. CONCLUSIONS: The somatosensory N140 passively increased even if subjects tried to attend actively to the stimulus source when the deviant alone condition was used. This change in N140 amplitude may be related to a strong orienting effect against a 'silent' background. SIGNIFICANCE: The present study provided evidence that the N140 is an indicator of passive attention against a silent background when the deviant alone condition or long interstimulus interval was used.

Adult↗

PubMedDate not supplied

Time-of-day-induced priming effects on verbal and nonverbal dichotic tasks in male and female adult subjects.

Normal adults (32 males and 32 females) were tested for time-of-day related shifts in laterality and priming on two dichotic listening tasks using consonant-vowel combinations (CVs) and musical melodies. The predicted time-of-day effect on melodies was due to males showing low report in the morning, but not the afternoon, suggesting increased right hemisphere involvement in the afternoon. A time-of-day-induced priming effect on the laterality index for CVs differentiated males and females. Males tested morning-first were more lateralized than females, who in turn were more lateralized when tested afternoon-first. A time-of-day-induced priming effect on the laterality index for music indicated those tested afternoon-first showed an overall left ear advantage (LEA), whereas those tested morning-first showed an overall right ear advantage (REA). On raw music scores a sex-linked, time-of-day-induced priming effect was due to the prior presentation of CVs--that is, cognitive priming. Other priming effects on music were evident for order of stimulus presentation and order of ear attended. Implications for theory, research and pedagogy are discussed.

Adult↗