Short-term incidental memory for irrelevant cues

A new analysis of previously published studies of delayed matching-to-sample (DMTS) water-escape and the results of a new food-reinforced discrimination study are presented. In both cases, male Sprague-Dawley rats demonstrated short-term incidental memory for irrelevant cues in the context of two-alternative forced-choice problems that required learning about relevant cues. In the DMTS experiments, relevant and irrelevant cues were place or brightness. In the discrimination experiment, the relevant cues were place, brightness or a visual-tactile maze insert. In all experiments, after the rats attained high-level performance, consistently making choices with respect to the relevant stimuli, response latencies to the correct relevant cue were shorter when the irrelevant cue value(s) was the same as on the immediately preceding trial. These latency differences are interpreted as indicating that the rats demonstrated short-term incidental memory for the irrelevant cues. This mnemonic phenomenon resembles priming, an implicit form of memory.     

Processing Irrelevant Location Information: Practice and Transfer Effects in a Simon Task

How humans produce cognitively driven fine motor movements is a question of fundamental importance in how we interact with the world around us. For example, we are exposed to a constant stream of information and we must select the information that is most relevant by which to guide our actions. In the present study, we employed a well-known behavioral assay called the Simon task to better understand how humans are able to learn to filter out irrelevant information. We trained subjects for four days with a visual stimulus presented, alternately, in central and lateral locations. Subjects responded with one hand moving a joystick in either the left or right direction. They were instructed to ignore the irrelevant location information and respond based on color (e.g. red to the right and green to the left). On the fifth day, an additional testing session was conducted where the task changed and the subjects had to respond by shape (e.g. triangle to the right and rectangle to the left). They were instructed to ignore the color and location, and respond based solely on the task relevant shape. We found that the magnitude of the Simon effect decreases with training, however it returns in the first few trials after a break. Furthermore, task-defined associations between response direction and color did not significantly affect the Simon effect based on shape, and no significant associative learning from the specific stimulus-response features was found for the centrally located stimuli. We discuss how these results are consistent with a model involving route suppression/gating of the irrelevant location information. Much of the learning seems to be driven by subjects learning to suppress irrelevant location information, however, this seems to be an active inhibition process that requires a few trials of experience to engage.     

Distributed attention and focused attention: different modalities of use

In the present experiments two different attention modalities were investigated: focused and distributed attention. In Experiment 1 manual choice reaction times to lateralized visual stimuli were measured. Visual stimuli (rectangles or squares) were presented in one of six positions along the horizontal axis. In between each position a digit 1 to 5 was permanently displayed. The subjects were instructed to switch their attention to one of the five digits and to respond as fast as possible to the stimulus target flashed either on the right or on the left of the focus of attention. The only difference in Experiment 2 was that the digit stayed on 100 msec only. The results show the importance of a visual cue (Exp. 1) for focused attention. In the absence of a permanent visual cue (Exp. 2) only distributed attention can be employed.     

Sexual and interhemispheric differences in the involvement of serotonin from the hippocampus and amygdaloid body in the processing of new and repeatedly presented information in rats]

Effects of novel or relevant (a single exposure to experimental chamber) and irrelevant (20 exposures to experimental chamber) stimuli on the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the left and right hippocamp and amygdala were studied in male and female rats. It was found that hemispheric specificity of 5-HT metabolism in hippocampus and amygdala depended on sex and novelty of information. In male rats, the hippocampal level of 5-HT in response to the novel stimulus increased in the left hemisphere, and the 5-HIAA hippocampal level increased bilaterally in response to irrelevant stimulus. In females, an increase in 5-HT and/or 5-HIAA levels was observed only in the left hippocampus in response both to relevant and irrelevant stimuli. In the amygdala, a hemispheric asymmetry of the 5-HT involvement, due to right-hemispheric changes in 5-HT metabolism, was observed only in male rats. In females, an increase in 5-HT level was found in the left and right amygdalas in response to irrelevant stimulus. These data suggest that serotonergic neurotransmitter mechanisms are an important factor which determines hemispheric and sex differences in selective attention.     

Directional and anteroposterior asymmetry of common white markings in the legs of the Arabian horse: response to selection

Arabian bay horses manifest, on the average, more common white markings in their hind legs than their forelegs (anteroposterior asymmetry) and more common white markings in their left legs than their right legs (directional asymmetry). To determine if genetic variation exists for these types of asymmetry, the phenotypic response was studied in bay foals when their dams and sires were selected for the directions of fore-hind and left-right differences. In the fore-hind studies, the quantitative shifts in the bay foals were in the direction specified by the selection scheme and the observed deviations were all statistically significant. The shifts were also consistently in the direction favored by selection in the left-right studies, but only two of six observed deviations were statistically significant using a one-tailed test of significance. Thus, only marginal statistical evidence is available to support the observed consistent responses to selection in the left-right studies. These differential responses are reflected in the magnitudes of the heritability estimates. Based on the overall results, it is concluded that both types of asymmetry have a genetic basis in the Arabian horse, but much more genetic variation is present for anteroposterior asymmetry than for directional asymmetry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mapping Proprioception across a 2D Horizontal Workspace

Relatively few studies have been reported that document how proprioception varies across the workspace of the human arm. Here we examined proprioceptive function across a horizontal planar workspace, using a new method that avoids active movement and interactions with other sensory modalities. We systematically mapped both proprioceptive acuity (sensitivity to hand position change) and bias (perceived location of the hand), across a horizontal-plane 2D workspace. Proprioception of both the left and right arms was tested at nine workspace locations and in 2 orthogonal directions (left-right and forwards-backwards). Subjects made repeated judgments about the position of their hand with respect to a remembered proprioceptive reference position, while grasping the handle of a robotic linkage that passively moved their hand to each judgement location. To rule out the possibility that the memory component of the proprioceptive testing procedure may have influenced our results, we repeated the procedure in a second experiment using a persistent visual reference position. Both methods resulted in qualitatively similar findings. Proprioception is not uniform across the workspace. Acuity was greater for limb configurations in which the hand was closer to the body, and was greater in a forward-backward direction than in a left-right direction. A robust difference in proprioceptive bias was observed across both experiments. At all workspace locations, the left hand was perceived to be to the left of its actual position, and the right hand was perceived to be to the right of its actual position. Finally, bias was smaller for hand positions closer to the body. The results of this study provide a systematic map of proprioceptive acuity and bias across the workspace of the limb that may be used to augment computational models of sensory-motor control, and to inform clinical assessment of sensory function in patients with sensory-motor deficits.     

Learning of colour and position cues in domestic chicks: Males are better at position,females at colour

Male and female chicks were trained to discriminate between two boxes for food reinforcement. The correct box was indicated by a colour cue (red or brown) and a position cue (right or left). After learning, the colour and the position cues were dissociated: the right-left location of the two boxes was alternated between trials according to a semi-random sequence.The chicks were thus retrained to discriminate either on the basis of colour (irrespective of position) or on the basis of position (irrespective of colour). There were no sex differences, during training, with both position and colour cues. However, during re-training females performed better on the colour learning task and males performed better on the position learning task.     

Systemic Organization of Perceptive Activity in Children with Different Levels of Mental Development

Visual evoked potentials (EPs) of the left and right hemispheres in response to relevant and irrelevant stimuli in the structures of the left and right hemispheres have been studied in healthy young schoolchildren, learning-disabled (LD) children, and mentally retarded (MR) children. In healthy children, the largest EP variations depending on the stimulus relevancy have been found in associative structures of the left hemisphere. In LD children of the same age, the amplitude and temporal characteristics of left-hemispheric EPs to target and nontarget stimuli are the same. In MR children, EPs to relevant and irrelevant stimuli do not differ from each other in either the left or the right hemisphere. EP latencies are significantly longer in MR children than in healthy children. The results of simultaneous recording of EPs in the left and right hemispheres during isolated stimulation of the right and left visual half-fields indicate that interhemispheric interaction is impaired in children with deviations in mental development. The results of the study are discussed in terms of the psychological characteristics and learning ability of children.     

Adjustment errors of feedback guided human forearm movements elicited by random position signal sequences

The effects of visual and auditory relevant feedback on human forearm movements elicited by random position signal sequences were examined. We observed the adjustment error sequences when the arm moved briskly and accurately to the target position. As the results, the mean adjustment errors for each speed (clock interval) of random position signal sequence are different in the left-right target positions, and also different in the flexion-extension movements. In faster speed (1s), the adjustment errors are approximately flat as compared with those in other speeds, on the other hand, in moderate speed (2s) or slower speed (3s), these indicate a upward tendency from left to right positions, and also indicate a upward tendency from flexion to extension movements. However, in the reaction times, the moving times, and the adjusting times, there are no significant differences for the left-right target positions and for the flexion-extension movements.     

Effects of sex factors and hemispheric localization on the involvement of serotonin from the frontal cortex, striatum, and nucleus accumbens into the processing of novel and repeatedly presented information in rats

The effects of novel or relevant (a single exposure to experimental chamber) and irrelevant (20 exposures to experimental chamber) stimuli on the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex, striatum, and nucleus accumbens in the left and right hemispheres were studied in male and female rats. It was found that 5-HT and 5-HIAA contents in the frontal cortex changed in response to neither relevant nor irrelevant stimuli. However, there were hemispheric difference in 5-HT and 5-HIAA in the frontal cortex of intact animals. The level of 5-HT in males and the level of 5-HIAA in females were higher in the left frontal cortex. In females, the level of 5-HIAA in the left striatum decreased in response to the novel stimulus. Sex differences in: a) 5-HT metabolism (increase in the level of 5-HIAA in males and increase in 5-HT in females) and b) lateralization (the striatal 5-HT metabolism in males changed bilaterally and only in the left hemisphere in females) were observed in reactions to irrelevant stimuli. Both in male and female rats, serotonin content in the nucleus accumbens changed only in response to the irrelevant stimuli. The 5-HT level increased in the left and right hemispheres independently of sex, but hemispheric difference was revealed only in females, in which the serotonin level was higher in the left nucleus accumbens. It is concluded that serotonergic neurotransmitter mechanisms are involved in hemispheric and sex differences in selective attention.     

Load detection and discrimination in a catching task: Role of haptic and auditory information

The aim of this study was to verify the contribution of haptic and auditory cues in the quick discrimination of an object mass. Ten subjects had to brake with the right hand the movement of a cup due to the falling impact of an object that could be of two different masses. They were asked to perform a quick left hand movement if the object was of the prescribed mass according to the proprioceptive and auditory cues they received from object contact with the cup and did not react to the other object. Three conditions were established: with both proprioceptive and auditory cues, only with proprioceptive cue or only with an auditory cue. When proprioceptive information was available subjects advanced responses time to the impact of the heavy object as compared with that of the light object. The addition of an auditory cue did not improve the advancement for the heavy object. We conclude that when a motor response has to be chosen according to different combinations of auditory and proprioceptive load-related information, subjects used mainly haptic information to fast respond and that auditory cues do not add relevant information that could ameliorate the quickness of a correct response.     

Rats' memory for event duration: differential effects of delaying the discriminative choice cue as opposed to the opportunity to execute the choice response

Rats were trained to discriminate short or long durations of houselight illumination using a choice procedure. During the test phase of each trial, the left and right levers were presented with an auditory cue above one of them on (cued lever) while the other was off (uncued lever). The auditory cue was presented immediately after sample offset and the levers were inserted after the auditory cue had been presented for 2 s. For half of the rats, the correct response following the short sample was to press the cued lever, while following the long sample, it was to press the uncued lever. This was reversed for the remaining rats. Following acquisition of the discrimination, two different types of delay tests were administered. In the first set, the delay between offset of the sample and onset of the auditory cue was manipulated (Cue Delay Test). In the second set, the delay between onset of the auditory cue and entry of the levers into the chamber was manipulated (Response Delay Test). Cue Delay testing resulted in a choose-long bias at the longer delays. Response Delay testing did not result in a systematic response bias and there was little forgetting over the delay interval. These data suggest that the rats did not stop the internal clock when the nominal sample was offset, but allowed it to keep running until the auditory cue was presented. The data from the Response Delay Test indicate that either a response decision was made based on the clock reading as soon as the auditory cue was presented, or the clock reading itself was retained over the delay with no subjective shortening and little forgetting.     

Modeling the relation between cardiac pump function and myofiber mechanics

Complexity of the geometry and structure of the heart hampers easy modeling of cardiac mechanics. The modeling can however be simplified considerably when using the hypothesis that in the normal heart myofiber structure and geometry adapt, until load is evenly distributed. A simple and realistic relationship is found between the hemodynamic variables cavity pressure and volume, and myofiber load parameters stress and strain. The most important geometric parameter in the latter relation is the ratio of cavity volume to wall volume, while actual geometry appears practically irrelevant. Applying the found relationship, a realistic maximum is set to left ventricular pressure after chronic pressure load. Pressures exceeding this level are likely to cause decompensation and heart failure. Furthermore, model is presented to simulate left and right ventricular pump function with left-right interaction.     

Pavlovian reward prediction and receipt in schizophrenia: relationship to anhedonia

Reward processing abnormalities have been implicated in the pathophysiology of negative symptoms such as anhedonia and avolition in schizophrenia. However, studies examining neural responses to reward anticipation and receipt have largely relied on instrumental tasks, which may confound reward processing abnormalities with deficits in response selection and execution. 25 chronic, medicated outpatients with schizophrenia and 20 healthy controls underwent functional magnetic resonance imaging using a pavlovian reward prediction paradigm with no response requirements. Subjects passively viewed cues that predicted subsequent receipt of monetary reward or non-reward, and blood-oxygen-level-dependent signal was measured at the time of cue presentation and receipt. At the group level, neural responses to both reward anticipation and receipt were largely similar between groups. At the time of cue presentation, striatal anticipatory responses did not differ between patients and controls. Right anterior insula demonstrated greater activation for nonreward than reward cues in controls, and for reward than nonreward cues in patients. At the time of receipt, robust responses to receipt of reward vs. nonreward were seen in striatum, midbrain, and frontal cortex in both groups. Furthermore, both groups demonstrated responses to unexpected versus expected outcomes in cortical areas including bilateral dorsolateral prefrontal cortex. Individual difference analyses in patients revealed an association between physical anhedonia and activity in ventral striatum and ventromedial prefrontal cortex during anticipation of reward, in which greater anhedonia severity was associated with reduced activation to money versus no-money cues. In ventromedial prefrontal cortex, this relationship held among both controls and patients, suggesting a relationship between anticipatory activity and anhedonia irrespective of diagnosis. These findings suggest that in the absence of response requirements, brain responses to reward receipt are largely intact in medicated individuals with chronic schizophrenia, while reward anticipation responses in left ventral striatum are reduced in those patients with greater anhedonia severity.     

Does the perception of moving eyes trigger reflexive visual orienting in autism?

Does movement of the eyes in one or another direction function as an automatic attentional cue to a location of interest? Two experiments explored the directional movement of the eyes in a full face for speed of detection of an aftercoming location target in young people with autism and in control participants. Our aim was to investigate whether a low-level perceptual impairment underlies the delay in gaze following characteristic of autism. The participants'' task was to detect a target appearing on the left or right of the screen either 100 ms or 800 ms after a face cue appeared with eyes averting to the left or right. Despite instructions to ignore eye-movement in the face cue, people with autism and control adolescents were quicker to detect targets that had been preceded by an eye movement cue congruent with target location compared with targets preceded by an incongruent eye movement cue. The attention shifts are thought to be reflexive because the cue was to be ignored, and because the effect was found even when cue-target duration was short (100 ms). Because (experiment two) the effect persisted even when the face was inverted, it would seem that the direction of movement of eyes can provide a powerful (involuntary) cue to a location.     

The parapineal mediates left-right asymmetry in the zebrafish diencephalon

The dorsal diencephalon (or epithalamus) of larval zebrafish displays distinct left-right asymmetries. The pineal complex consists of the pineal organ anlage and an unpaired, left-sided accessory organ - the parapineal. The neighboring brain nuclei, the left and right dorsal habenulae, show consistent differences in their size, density of neuropil and gene expression. Mutational analyses demonstrate a correlation between the left-right position of the parapineal and the laterality of the habenular nuclei. We show that selective ablation of the parapineal organ results in the loss of habenular asymmetry. The left-sided parapineal therefore influences the left-right identity of adjacent brain nuclei, indicating that laterality of the dorsal diencephalon arises in a step-wise fashion.     

Bilateral field advantage in visual enumeration

A number of recent studies have demonstrated superior visual processing when the information is distributed across the left and right visual fields than if the information is presented in a single hemifield (the bilateral field advantage). This effect is thought to reflect independent attentional resources in the two hemifields and the capacity of the neural responses to the left and right hemifields to process visual information in parallel. Here, we examined whether a bilateral field advantage can also be observed in a high-level visual task that requires the information from both hemifields to be combined. To this end, we used a visual enumeration task--a task that requires the assimilation of separate visual items into a single quantity--where the to-be-enumerated items were either presented in one hemifield or distributed between the two visual fields. We found that enumerating large number (>4 items), but not small number (<4 items), exhibited the bilateral field advantage: enumeration was more accurate when the visual items were split between the left and right hemifields than when they were all presented within the same hemifield. Control experiments further showed that this effect could not be attributed to a horizontal alignment advantage of the items in the visual field, or to a retinal stimulation difference between the unilateral and bilateral displays. These results suggest that a bilateral field advantage can arise when the visual task involves inter-hemispheric integration. This is in line with previous research and theory indicating that, when the visual task is attentionally demanding, parallel processing by the neural responses to the left and right hemifields can expand the capacity of visual information processing.     

Effects of attention and emotion on face processing in the human brain: an event-related fMRI study.

We used event-related fMRI to assess whether brain responses to fearful versus neutral faces are modulated by spatial attention. Subjects performed a demanding matching task for pairs of stimuli at prespecified locations, in the presence of task-irrelevant stimuli at other locations. Faces or houses unpredictably appeared at the relevant or irrelevant locations, while the faces had either fearful or neutral expressions. Activation of fusiform gyri by faces was strongly affected by attentional condition, but the left amygdala response to fearful faces was not. Right fusiform activity was greater for fearful than neutral faces, independently of the attention effect on this region. These results reveal differential influences on face processing from attention and emotion, with the amygdala response to threat-related expressions unaffected by a manipulation of attention that strongly modulates the fusiform response to faces.     

Left-right positioning of the adult rudiment in sea urchin larvae is directed by the right side.

Indirect-developing sea urchins eventually form an adult rudiment on the left side through differential left-right development in the late larval stages. Components of the adult rudiment, such as the hydropore canal, the hydrocoel and the primary vestibule, all develop on the left side alone, and are the initial morphological traits that exhibit left-right differences. Although it has previously been shown that partial embryos dissected in cleavage stages correctly determine the normal left-right placement of the adult rudiment, the timing and the mechanism that determine left-right polarity during normal development remain unknown. In order to determine these, we have carried out a series of regional operations in two indirect-developing sea urchin species. We excised all or a part of tissue on the left or right side of the embryos during the early gastrula stage and the two-armed pluteus stage, and examined the left-right position of the adult rudiment, and of its components. Excisions of tissues on the left side of the embryos, regardless of stage, resulted in formation of a left adult rudiment, as in normal development. By contrast, excisions on the right side of the embryos resulted in three different types of impairment in the left-right placement of the adult rudiment in a stage-dependent manner. Generally, when the adult rudiment was definitively formed only on the right side of the larvae, no trace of basic development of the components of the adult rudiment was found on the left side, indicating that a right adult rudiment results from reversal of the initial left-right polarity but not from a later inhibitory effect on the development of an adult rudiment. Thus, we suggest that determination of the left-right placement of the adult rudiment depends on a process, which is directed by the right side, of polarity establishment during the gastrula and the prism stages; however, but commitment of the cell fate to initiate formation of the adult rudiment occurs later than the two-armed pluteus stage.     

Marijuana: Differential effects on right and left hemisphere functions in man

Marijuana, smoked at moderate doses, produced a differential impairment of the reaction times of right-handed males to pictorial stimuli presented to the left and right cerebral hemispheres. After smoking marijuana responses to pictorial stimuli presented to the right hemisphere were slowed significantly less than to the left hemisphere. Responses to verbal stimuli (trigrams) were slowd equally in both hemispheres, preserving an initial left hemisphere superiority for this material. This suggests that marijuana may differentially change the processing speed or relative dominance of man's two cerebral hemispheres, depending on the nature of the material being processed.