Disruptive effects of prefeeding and haloperidol administration on multiple measures of food-maintained behavior in rats

Four rats responded under a choice reaction-time procedure. At the beginning of each trial, the rats were required to hold down a center lever for a variable duration, release it following a high- or low-pitched tone, and press either a left or right lever, conditionally on the tone. Correct choices were reinforced with a probability of .95 or .05 under blinking or static houselights, respectively. After performance stabilized, disruptive effects of free access to food pellets prior to sessions (prefeeding) and intraperitoneal injection of haloperidol were examined on multiple behavioral measures (i.e., the number of trials completed, percent of correct responses, and reaction time). Resistance to prefeeding depended on the probability of food delivery for the number of trials completed and reaction time. Resistance to haloperidol, on the other hand, was not systematically affected by the probability of food delivery for all dependent measures.     

Spatial compatibility and position of the effectors

Mean reaction times obtained with crossed hands (right had on the left and left hand on the right) are slower than reaction times obtained with uncrossed hands (right hand on the right and left hand on the left). These results have been explained as a compatibility effect between the responding hand and its spatial position. The goal of the present experiment was to establish whether the position of the hand is encoded by the subjects relative to their body (absolute position) or relative to the other hand (relative position). The subjects performed a discrimination task on two visual stimuli. Stimuli and hands were either on the same side of the body (both on the left or both on the right) or had different absolute position. In all conditions the subjects responded with crossed and uncrossed hands. The results support the hypothesis that relative position is encoded.     

Hemispheric lateralization of visuo-spatial function in man

Two parts of a geometrical figure are consecutively presented to healthy adult subjects in the left and right visual fields; the subjects have to compare them mentally and to decide whether these parts form a standard figure or not. Correctness of the reaction is controlled by a computer which lights up on the screen the words "good" or "error". The number of correct decisions of this visual-spatial task does not depend on the hemisphere to which information is addressed. The reaction time is substantially shorter if the information comes "directly" to the right hemisphere. Due to better training in the left hemisphere interhemispheric difference in reaction time gradually disappears in repeated tests. Training to mental "constructing" takes place only in the tests following positive feedback stimulus. Analysis of amplitude-temporal parameters of P300 wave shows that at correct decision of the visual-spatial task the level of activation in the right hemisphere is higher than in the left one.     

Asymmetry of the cerebral hemispheres during comparison of paired visual stimuli

In conditions of tachistoscopic presentation of visual stimuli, healthy (male and female) right-handed subjects carried out a paired comparison of the stimuli presented unilaterally and in the center of the visual field. In case of recognition of images of words and objects, the number of correct answers and motor reaction time usually did not significantly differ at two interstimuli intervals (1 and 10 s). In comparing images of faces, there also were no differences by the number of reactions, and the reaction time was less at the intervals of 1 s. The left hemisphere dominated at the identification of words and female faces, the right one--at the recognition of male faces. When the right visual field was stimulated images of various classes were recognized more differentially than at the stimulation of the left visual field. The male subjects had more prominent interhemispheric differences than the females. The increase of the interstimuli interval from 1 to 10 s brought to a weakening of the functional interhemispheric asymmetry and decreasing of the differences between the male and female subjects. The obtained data show that in the processes connected with short-time memory, functional interhemispheric asymmetry is basically formed at the initial stages of the information processing.     

Interhemispheric interactions between the human primary somatosensory cortices

In the somatosensory domain it is still unclear at which processing stage information reaches the opposite hemispheres. Due to dense transcallosal connections, the secondary somatosensory cortex (S2) has been proposed to be the key candidate for interhemispheric information transfer. However, recent animal studies showed that the primary somatosensory cortex (S1) might as well account for interhemispheric information transfer. Using paired median nerve somatosensory evoked potential recordings in humans we tested the hypothesis that interhemispheric inhibitory interactions in the somatosensory system occur already in an early cortical processing stage such as S1. Conditioning right S1 by electrical median nerve (MN) stimulation of the left MN (CS) resulted in a significant reduction of the N20 response in the target (left) S1 relative to a test stimulus (TS) to the right MN alone when the interstimulus interval between CS and TS was between 20 and 25 ms. No such changes were observed for later cortical components such as the N20/P25, N30, P40 and N60 amplitude. Additionally, the subcortically generated P14 response in left S1 was also not affected. These results document the existence of interhemispheric inhibitory interactions between S1 in human subjects in the critical time interval of 20-25 ms after median nerve stimulation.     

Interhemispheric Interaction during Memorization of Movement Rhythm

After memorizing a simple periodical movement in the ankle joint, 36 healthy subjects (right-handers) reproduced it from memory. The movement rhythm image that formed during movement in the left ankle joint was memorized better than when the movement was performed by the right extremity. The specific features of interhemispheric interaction at various stages of trace processes, unequal participation of the hemispheres in perception and processing of information, and the physiological expedience of the signal transmission from the right to the left hemisphere are sufficient to assume a basic sequence of hemispheric functional activity redistribution when the brain masters new cognitive actions.     

Spatial frames of reference and somatosensory processing: a neuropsychological perspective.

In patients with lesions in the right hemisphere, frequently involving the posterior parietal regions, left-sided somatosensory (and visual and motor) deficits not only reflect a disorder of primary sensory processes, but also have a higher-order component related to a defective spatial representation of the body. This additional factor, related to right brain damage, is clinically relevant: contralesional hemianaesthesia (and hemianopia and hemiplegia) is more frequent in right brain-damaged patients than in patients with damage to the left side of the brain. Three main lines of investigation suggest the existence of this higher-order pathological factor. (i) Right brain-damaged patients with left hemineglect may show physiological evidence of preserved processing of somatosensory stimuli, of which they are not aware. Similar results have been obtained in the visual domain. (ii) Direction-specific vestibular, visual optokinetic and somatosensory or proprioceptive stimulations may displace spatial frames of reference in right brain-damaged patients with left hemineglect, reducing or increasing the extent of the patients'' ipsilesional rightward directional error, and bring about similar directional effects in normal subjects. These stimulations, which may improve or worsen a number of manifestations of the neglect syndrome (such as extrapersonal and personal hemineglect), have similar effects on the severity of left somatosensory deficits (defective detection of tactile stimuli, position sense disorders). However, visuospatial hemineglect and the somatosensory deficits improved by these stimulations are independent, albeit related, disorders. (iii) The severity of left somatosensory deficits is affected by the spatial position of body segments, with reference to the midsagittal plane of the trunk. A general implication of these observations is that spatial (non-somatotopic) levels of representation contribute to corporeal awareness. The neural basis of these spatial frames includes the posterior parietal and the premotor frontal regions. These spatial representations could provide perceptual-premotor interfaces for the organization of movements (e.g. pointing, locomotion) directed towards targets in personal and extrapersonal space. In line with this view, there is evidence that the sensory stimulations that modulate left somatosensory deficits affect left motor disorders in a similar, direction-specific, fashion.     

Hemispheric asymmetries in cortical electrical activity during sleep. I

The hypothesis of a predominance of the right hemisphere in stage REM as compared to NREM has been tested through a spectral analysis of the EEG recorded from left (T3) and right (T4) temporal sites in 5 young healthy right-handed male subjects. Variations in the asymmetry coefficient R - L/R + L in different sleep stages have been analyzed by one way ANOVAs and Sheffé's tests. The hypothesis of a progressive increase in left hemisphere activity throughout different REM cycles as one approaches final awakenings have been investigated by comparing variations in the asymmetry coefficient for epochs of REM and stage 2 NREM sampled in different phases of the REM cycle. EEG results do not support either the hypothesized stage dependent or cycle dependent variation in EEG activity during sleep. We question whether variations in EEG amplitude and synchronization can be used as indices of hemispheric asymmetries during sleep.     

A psychophysiological analysis of the cognitive tempo by means of evoked potentials

A new approach to measure the speed of cognitive behaviour is introduced. The decomposition of reaction time allows to identify different stages: perception, comparison steps and motoric organization. For this reason the additive factor method and the analysis of event-related potentials is used. The results show specific decelerations in elderly subjects and alcoholics. The application of the method in clinical psychodiagnostic and psychopharmacology is discussed.     

Attentional weighting: a possible account of visual field asymmetries in visual search?

Several previous visual search studies measuring reaction times have demonstrated scanning biases across the visual field (i.e. a tendency to begin a serial search in a particular region of space). In the present study, we measured visual discrimination thresholds for a target presented amongst distractors using displays that were short enough to greatly reduce the potential for serial (i.e. scanning) search. For both a motion and orientation task, subjects' performance was significantly better when the target appeared in the inferior, as compared to the superior, visual field (no differences were observed between left and right visual fields). These findings suggest that subjects may divide attention unevenly across the visual field when searching for a target amongst distractors, a phenomenon we refer to as 'attentional weighting'. To rule out the possibility that these visual field asymmetries were sensory in nature, thresholds were also measured for conditions in which subjects' attention was directed to the location of the target stimulus, either because it was presented alone in the display or because a spatial cue directed subjects' attention to the location of that target presented amongst distractors. Under these conditions, visual field asymmetries were smaller (or non-existent), suggesting that sensory factors (such as crowding) are unlikely to account for our results. In addition, analyses of set-size effects (obtained by comparing thresholds for a single target vs. the target presented amongst distractors) could be accounted for by an unlimited capacity model, suggesting that multiple stimuli can be processed simultaneously without any limitations at an early stage of sensory processing. Taken together, these findings suggest the possible existence of biases in attentional weighting at a late stage of processing. The bias appears to favor the inferior visual field, which may arise from the fact that there is more ecologically-relevant information in this region of space.     

Interhemispheric asymmetry of positive emotional reactions in rats

Interhemispheric asymmetry of positive emotional reactions was studied in rats: satisfaction of drinking need and self-stimulation. Successive inactivation of the hemispheres was carried out by potassium spreading depression. Switching off of the right as well as the left hemispheres symmetrically influenced the whole quantity of the water, drunk by the rats to a full thirst satisfaction, i. e. the magnitude of need. However, at different stages of drinking need satisfaction an interhemispheric asymmetry was observed: under a strong drinking motivation the right hemisphere dominated, under a weak motivation--the left one. Switching off of the right hemisphere lowered the frequency of self-stimulation of the lateral hypothalamus and switching off the left one heightened it, testifying to the dominance of the right hemisphere in the reaction of self-stimulation. This reaction was also characterized by asymmetry of the lateral hypothalamus nuclei; reactivity to hemispheres inactivation (decreasing or increasing of self-stimulation frequency) of the right nucleus was more expressed than that of the left one.     

Delayed matching-to-position performance in C57BL/6N mice

Delayed matching-to-sample is one of the most frequently employed behavioral tasks for assessing spatial working memory in animals. Although the advantages of the task have been widely acknowledged and it is used in the study of a variety of species, its application to mice has been rare. In the present study, we reported the efficacy of a delayed matching-to-position task in C57BL mice lever-pressing in an operant-conditioning chamber. Each trial started with the press of a back lever, followed by the presentation of either a left or right front lever. When the ratio requirement for presses to the front lever (sample) was met, a delay interval started. Delay interval continued until the mice made the first response after the elapse of the programmed delay interval. This was followed by the presentation of a choice of left or right front levers. The choice of the same front lever as the sample was reinforced, whereas the other was not. The proportion of correct choices showed a delay-dependent decrement. A higher ratio of response requirement to the sample resulted in increased accuracy, but the duration of the intertrial interval had no effect. Preceding trials also influenced response accuracy, indicating proactive interference. Overall, the results replicated the effects of parametric manipulations reported in other species, and thus, our findings validate the efficacy of the task for assessing spatial working memory in laboratory mice.     

The cortical interactions in short time intervals during the search for verbal associations

Cortical connectivity was studied in tasks of generating the use of words in comparison with reading aloud the same words. These tasks were used earlier in PET and high-density ERP recording studies, which described both the functional anatomy and time course of involvement of cortical areas in word processing. We developed a new method for studying the synchrony of EEG spectral components within the short time intervals compatible with the duration of particular cognitive operations. The wavelet transform of the ERP records and calculation of correlations between the wavelet curves were used to reveal connections between cortical areas. Three stages of intracortical communications developing over the course of task performance were discovered: between the right and left frontal areas (0-200 ms after the stimulus presentation), between the left frontal and left posterior temporo-parietal areas (250-500 ms), and, finally, between the left temporal and right fronto-centro-temporal areas. These findings are in good agreement with the results of the previous PET and ERP studies and supplement them with the circuitry of cortical information transfer. Also, they suggest some differences in information processing during automated reading and performance of more complicated use-generation task.     

Can ambient odors influence the recognition of emotional words? A behavioral and event-related potentials study

Odor context can affect the recognition of facial expressions. However, there is no evidence to date that odor can regulate the processing of emotional words conveyed by visual words. An emotional word recognition task was combined with event-related potential technology. Briefly, 49 adults were randomly divided into three odor contexts (pleasant odor, unpleasant odor, and no odor) to judge the valence of emotional words (positive, negative, and neutral). Both behavioral and Electroencephalography (EEG) data were collected. Both the pleasant odor and unpleasant odor contexts shortened the response time of the subjects to emotional words. In addition, negative words induced greater amplitudes of early posterior negativity (EPN) and late positive potential (LPP) than the positive and neutral words. However, the neutral words induced a larger N400 amplitude than the positive and negative words. More importantly, the processing of emotional words was found to be modulated by external odor contexts. For example, during the earlier (P2) processing stages, pleasant and unpleasant odor contexts induced greater P2 amplitudes than the no odor context. In the unpleasant odor context, negative words with the same odor valence induced greater P2 amplitudes than the positive words. During the later (N400) stages, various regions of the brain regions exhibited different results. For example, in the left and right frontal areas of the brain, exposure to positive words in a pleasant odor context resulted in a smaller N400 amplitude than exposure to neutral words in the same context. Meanwhile, in the left and right central regions, emotional words with the same valence as pleasant or unpleasant odor contexts elicited the minimum N400 amplitude. Individuals are very sensitive to emotional information. With deeper processing, different cognitive processes are reflected and they can be modulated by external odors. In the early and late stages of word processing, both pleasant and unpleasant odor contexts exhibited an undifferentiated dominance effect and could specifically modulate affectively congruent words.     

Lateralized visual behavior in bottlenose dolphins (Tursiops truncatus) performing audio-visual tasks: the right visual field advantage

Analyzing cerebral asymmetries in various species helps in understanding brain organization. The left and right sides of the brain (lateralization) are involved in different cognitive and sensory functions. This study focuses on dolphin visual lateralization as expressed by spontaneous eye preference when performing a complex cognitive task; we examine lateralization when processing different visual stimuli displayed on an underwater touch-screen (two-dimensional figures, three-dimensional figures and dolphin/human video sequences). Three female bottlenose dolphins (Tursiops truncatus) were submitted to a 2-, 3- or 4-, choice visual/auditory discrimination problem, without any food reward: the subjects had to correctly match visual and acoustic stimuli together. In order to visualize and to touch the underwater target, the dolphins had to come close to the touch-screen and to position themselves using monocular vision (left or right eye) and/or binocular naso-ventral vision. The results showed an ability to associate simple visual forms and auditory information using an underwater touch-screen. Moreover, the subjects showed a spontaneous tendency to use monocular vision. Contrary to previous findings, our results did not clearly demonstrate right eye preference in spontaneous choice. However, the individuals' scores of correct answers were correlated with right eye vision, demonstrating the advantage of this visual field in visual information processing and suggesting a left hemispheric dominance. We also demonstrated that the nature of the presented visual stimulus does not seem to have any influence on the animals' monocular vision choice.     

Searching for the majority: algorithms of voluntary control

Voluntary control of information processing is crucial to allocate resources and prioritize the processes that are most important under a given situation; the algorithms underlying such control, however, are often not clear. We investigated possible algorithms of control for the performance of the majority function, in which participants searched for and identified one of two alternative categories (left or right pointing arrows) as composing the majority in each stimulus set. We manipulated the amount (set size of 1, 3, and 5) and content (ratio of left and right pointing arrows within a set) of the inputs to test competing hypotheses regarding mental operations for information processing. Using a novel measure based on computational load, we found that reaction time was best predicted by a grouping search algorithm as compared to alternative algorithms (i.e., exhaustive or self-terminating search). The grouping search algorithm involves sampling and resampling of the inputs before a decision is reached. These findings highlight the importance of investigating the implications of voluntary control via algorithms of mental operations.     

Reflection of the Emotional Significance of Visual Stimuli in the Characteristics of Evoked EEG Potentials

Healthy subjects (n = 88) were asked to passively visualize positive and passive emotiogenic visual stimuli and also stimuli with a neutral emotional content. Images of the International Affective Picture System (IAPS) were used. Amplitude/time characteristics of the components of evoked EEG potentials (EPs), P1, N1, P2, N2, and P3 and topographic distribution of the latter components were analyzed. The latencies, amplitudes, and topography of the EP waves induced by presentation of positive and negative stimuli were found to be different from the respective values for the EPs induced by neutral stimuli. The level and pattern of these differences typical of different EP components were dissimilar and depended on the sign of the emotions. Specificities related to the valency of an identified stimulus were observed within nearly all stages of processing of visual signals, for the negative stimuli, beginning from an early stage of sensory analysis corresponding to the development of wave Р1. The latencies of components Р1 in the case of presentation of emotiogenic negative stimuli and those of components N1, N2, and Р3 in the case of presentation of the stimuli of both valencies were shorter than the latencies observed at neutral stimuli. The amplitude of component N2 at perception of positive stimuli was, on average, lower, while the Р3 amplitude at perception of all emotiogenic stimuli was higher than in the case of presentation of neutral stimuli. The time dynamics of topographic peculiarities of processing of emotiogenic information were complicated. Activation of the left hemisphere was observed during the earliest stages of perception, while the right hemisphere was activated within the intermediate stages. Generalized activation of the cortex after the action of negative signals and dominance of the left hemisphere under conditions of presentation of positive stimuli were observed only within the final stages. As is supposed, emotiogenic stimuli possess a greater biological significance than neutral ones, and this is why the former attract visual attention first; they more intensely activate the respective cortical zones, and the corresponding visual information is processed more rapidly. The observed effects were more clearly expressed in the case of action of negative stimuli; these effects involved more extensive cortical zones. These facts are indicative of the higher intensity of activating influences of negative emotiogenic stimuli on neutral systems of the higher CNS structures.     

Assessment of recognition of emotions by healthy persons and patients with focal brain pathology

To assess the involvement of different structures of the human brain into successive stages of the recognition of the principal emotions by facial expression, we examined 48 patients with local brain lesions and 18 healthy adult subjects. It was shown that at the first (intuitive) stage of the recognition, premotor areas of the right hemisphere and temporal areas of the left hemisphere are of considerable importance in the recognition of both positive and negative emotions. In this process, the left temporal areas are substantially involved into the recognition of anger, and the right premotor areas predominantly participate in the recognition of fear. In patients with lesions of the right and left brain hemispheres, at the second (conscious) stage of recognition, the critical attitude to the assessment of emotions drops depending on the sign of the detected emotion. We have confirmed the hypothesis about a correlation between the personality features of the recognition of facial expressions and the dominant emotional state of a given subject.     

Altered spontaneous activity in anisometropic amblyopia subjects: revealed by resting-state FMRI

Amblyopia, also known as lazy eye, usually occurs during early childhood and results in poor or blurred vision. Recent neuroimaging studies have found cortical structural/functional abnormalities in amblyopia. However, until now, it was still not known whether the spontaneous activity of the brain changes in amblyopia subjects. In the present study, regional homogeneity (ReHo), a measure of the homogeneity of functional magnetic resonance imaging signals, was used for the first time to investigate changes in resting-state local spontaneous brain activity in individuals with anisometropic amblyopia. Compared with age- and gender-matched subjects with normal vision, the anisometropic amblyopia subjects showed decreased ReHo of spontaneous brain activity in the right precuneus, the left medial prefrontal cortex, the left inferior frontal gyrus, and the left cerebellum, and increased ReHo of spontaneous brain activity was found in the bilateral conjunction area of the postcentral and precentral gyri, the left paracentral lobule, the left superior temporal gyrus, the left fusiform gyrus, the conjunction area of the right insula, putamen and the right middle occipital gyrus. The observed decreases in ReHo may reflect decreased visuo-motor processing ability, and the increases in ReHo in the somatosensory cortices, the motor areas and the auditory area may indicate compensatory plasticity in amblyopia.     

Cerebral activation to intranasal chemosensory trigeminal stimulation

Although numerous functional magnetic resonance imaging (FMRI) studies have been performed on the processing of olfactory information, the intranasal trigeminal system so far has not received much attention. In the present study, we sought to delineate the neural correlates of trigeminal stimulation using carbon dioxide (CO(2)) presented to the left or right nostril. Fifteen right-handed men underwent FMRI using single runs of 3 conditions (CO(2) in the right and the left nostrils and an olfactory stimulant-phenyl ethyl alcohol-in the right nostril). As expected, olfactory activations were located in the orbitofrontal cortex (OFC), amygdala, and rostral insula. For trigeminal stimulation, activations were found in "trigeminal" and "olfactory" regions including the pre- and postcentral gyrus, the cerebellum, the ventrolateral thalamus, the insula, the contralateral piriform cortex, and the OFC. Left compared with right side stimulations resulted in stronger cerebellar and brain stem activations; right versus left stimulation resulted in stronger activations of the superior temporal sulcus and OFC. These results suggest a trigeminal processing system that taps into similar cortical regions and yet is separate from that of the olfactory system. The overlapping pattern of cortical activation for trigeminal and olfactory stimuli is assumed to be due to the intimate connections in the processing of information from the 2 major intranasal chemosensory systems.