Cognitive mechanisms of nicotine on visual attention

Understanding nicotine's neurobiological and cognitive mechanisms may help explain both its addictive properties and potential therapeutic applications. As such, functional MRI was used to determine the neural substrates of nicotine's effects on a sustained attention (rapid visual information-processing) task. Performance was associated with activation in a fronto-parietal-thalamic network in both smokers and nonsmokers. Along with subtle behavioral deficits, mildly abstinent smokers showed less task-induced brain activation in the parietal cortex and caudate than did nonsmokers. Transdermal nicotine replacement improved task performance in smokers and increased task-induced brain activation in the parietal cortex, thalamus, and caudate, while nicotine induced a generalized increase in occipital cortex activity. These data suggest that nicotine improves attention in smokers by enhancing activation in areas traditionally associated with visual attention, arousal, and motor activation.     

Neurophysiological mechanisms of voluntary attention: a review

The review is focused on attention as behavior-controlling process. Neurophysiological, electrophysiological and neuropsychological studies of different brain structures during voluntary attention are analyzed. These data show that selective voluntary attention modulates activity of sensory specific cortical zones involved in relevant signal processing. Fronto-thalamic system consisting of prefrontal cortex and thalamic mediodorsal nuclei is shown to be main source of top-down selective modulation of voluntary attention. The review proposed the hypothetical model of selective cortical activity modulation during voluntary attention based upon the available data and evidence of own electroencephalographic studies.     

Time course of attention reveals different mechanisms for spatial and feature-based attention in area V4

Attention can facilitate visual processing, emphasizing specific locations and highlighting stimuli containing specific features. To dissociate the mechanisms of spatial and feature-based attention, we compared the time course of visually evoked responses under different attention conditions. We recorded from single neurons in area V4 during a delayed match-to-sample task that controlled both spatial and feature-based attention. Neuronal responses increased when spatial attention was directed toward the receptive field and were modulated by the identity of the target of feature-based attention. Modulation by spatial attention was weaker during the early portion of the visual response and stronger during the later portion of the response. In contrast, modulation by feature-based attention was relatively constant throughout the response. It appears that stimulus onset transients disrupt spatial attention, but not feature attention. We conclude that spatial attention reflects a combination of stimulus-driven and goal-driven processes, while feature-based attention is purely goal driven.     

Opioid mechanisms in insects,with special attention toLeucophaea maderae

1. This review article provides information on the evolutionary history of neuroendocrine and related regulatory mechanisms. It focuses on the presence, diverse roles, and modes of operation of one class of neuropeptides, the endogenous opioids, in insects. 2. Opioid peptides, closely resembling those of vertebrates, have been identified in the brain and related neuroendocrine structures by means of immunocytochemistry and high-pressure liquid chromatography. 3. The demonstration of naloxone-sensitive, high-affinity binding sites for Met-enkephalin-like neuropeptides in the brain and digestive tract of Leucophaea deserves special attention because it provides new insights into the functional significance of opiate receptors paralleling those known in vertebrates. 4. Possible roles of receptor-mediated opioid systems in the insects discussed are regulation of the cyclicity of the female reproductive system, maintenance of normal midgut function mediated by the recurrent nerve, and locomotor activity.     

Searching for the neural mechanisms of feature-based attention in the primate brain

In this issue, two studies, one by Zhou and Desimone and another by Cohen and Maunsell, provide new insights into the mechanisms of feature-based attention (FBA). The former demonstrates a new role of the frontal eye fields in the origins of FBA and the latter shows that FBA is coordinated across both hemispheres.     

Role of the human thalamic parafascicular (CM-Pf) complex in neuronal mechanisms of selective attention

Responses of 93 single units of the human thalamic CM-Pf complex to relevant and irrelevant verbal (or sensory) stimuli were studied using microelectrode technique in alert diskinetic patients suffering from the tonic forms of spasmodic torticollis during 11 stereotaxic operations. The response patterns of two types units with irregular unitary (A-type) and low-threshold bursting Ca(2+)-dependent (B-type) spike activity were studied. Three main conclusions emerge from the studies: 1) high reactivity of both A- and B-units to presentation of relevant verbal stimuli with differences of their response patterns as determined by the type of constituent elements; 2) close functional connectivity of these neuronal changes with the level of selective attention; 3) at the moment of attention activation, the appearance of transient interneuronal interactions between adjacent A and B cells characterized by the local synchronization and stabilization of rhythmic oscillations. These data point to considerable contribution of the thalamic CM-Pf complex and its neuronal mechanisms into organization of the human selective attention and triggering verbal-related processing during performance of purposive speech-provoked voluntary acts.     

The cognitive neuroscience of visual attention.

In current conceptualizations of visual attention, selection takes place through integrated competition between recurrently connected visual processing networks. Selection, which facilitates the emergence of a 'winner' from among many potential targets, can be associated with particular spatial locations or object properties, and it can be modulated by both stimulus-driven and goal-driven factors. Recent neurobiological data support this account, revealing the activation of striate and extrastriate brain regions during conditions of competition. In addition, parietal and temporal cortices play a role in selection, biasing the ultimate outcome of the competition.     

A computational theory of visual attention.

A computational theory of visual attention is presented. The basic theory (TVA) combines the biased-choice model for single-stimulus recognition with the fixed-capacity independent race model (FIRM) for selection from multi-element displays. TVA organizes a large body of experimental findings on performance in visual recognition and attention tasks. A recent development (CTVA) combines TVA with a theory of perceptual grouping by proximity. CTVA explains effects of perceptual grouping and spatial distance between items in multi-element displays. A new account of spatial focusing is proposed in this paper. The account provides a framework for understanding visual search as an interplay between serial and parallel processes.     

Cross-modal links in spatial attention.

A great deal is now known about the effects of spatial attention within individual sensory modalities, especially for vision and audition. However, there has been little previous study of possible cross-modal links in attention. Here, we review recent findings from our own experiments on this topic, which reveal extensive spatial links between the modalities. An irrelevant but salient event presented within touch, audition, or vision, can attract covert spatial attention in the other modalities (with the one exception that visual events do not attract auditory attention when saccades are prevented). By shifting receptors in one modality relative to another, the spatial coordinates of these cross-modal interactions can be examined. For instance, when a hand is placed in a new position, stimulation of it now draws visual attention to a correspondingly different location, although some aspects of attention do not spatially remap in this way. Cross-modal links are also evident in voluntary shifts of attention. When a person strongly expects a target in one modality (e.g. audition) to appear in a particular location, their judgements improve at that location not only for the expected modality but also for other modalities (e.g. vision), even if events in the latter modality are somewhat more likely elsewhere. Finally, some of our experiments suggest that information from different sensory modalities may be integrated preattentively, to produce the multimodal internal spatial representations in which attention can be directed. Such preattentive cross-modal integration can, in some cases, produce helpful illusions that increase the efficiency of selective attention in complex scenes.     

Parallel processes within the 'spot-light' of attention.

Human ability to identify simultaneously two targets in the visual field is severely limited. Previous studies have shown that orientation identification of two targets takes twice the time needed for one target. Here we asked whether this seriality is imposed by the decision requirement of the task or by such stimulus properties as target spatial separation and similarity. Observers had to identify the orientations (vertical vs horizontal) of two Gabor patches presented at random positions. Performance on this double-task experiment was compared with performance on each of the tasks when carried out alone. We varied the spatial separation between the two targets for targets having identical or different spatial-frequencies and found that the orientation of two targets having different frequencies could be identified in parallel when occupying the same spatial position but not when separated in space by 4 deg of visual angle or more. Targets having the same frequency could be identified in parallel even when separated by 8 deg, demonstrating that decision factors do not impose seriality. This result can be taken as evidence for the existence of a grouping process operating prior to orientation identification. This grouping process operates according to classical Gestalt rules (proximity, similarity) and enables parallel attentive processing of large input chunks.     

Functional maturation of the brain and formation of the neurophysiological mechanisms of selective voluntary attention in young schoolchildren

A particular role was demonstrated for functional maturation of the frontothalamic system (FTS) of the brain in forming the cerebral organization of selective voluntary attention in ontogeny. Analysis of the coherence of the rhythmic components of the EEG α range in adults and seven-to eight-and nine-to ten-year-old children showed that, if the functional state of the control structures corresponds to the age, the formation of the neurophysiological mechanisms selectively modulating cortical activity and supporting selective tuning of the cerebral structures to the cognitive task is completed by the age of seven or eight years. Unlike adults, children demonstrated no interhemispheric features of the intercenter integration of cortical zones in the prestimulus period of voluntary attention. Children with a functionally immature FTS lacked selective specific integration of cortical zones in the pretuning period. The deficit of selective modulation of cortical activity in children with a functionally immature FTS is considered as the neurophysiological factor that delays the formation of voluntary attention and voluntary control of activity and, finally, leads to learning difficulties.     

Molecular mechanisms of schizophrenia.

Schizophrenia is a complex disorder, where family, twin and adoption studies have been demonstrating a high heritability of the disease and that this disease is not simply defined by several major genes but rather evolves from addition or potentiation of a specific cluster of genes, which subsequently determines the genetic vulnerability of an individual. Linkage and association studies suggest that a genetic vulnerablility, is not forcefully leading to the disease since triggering factors and environmental influences, i.e. birth complications, drug abuse, urban background or time of birth have been identified. This has lead to the assumption that schizophrenia is not only a genetically defined static disorder but a dynamic process leading to dysregulation of multiple pathways. There are several different hypothesis based on several facets of the disease, some of them due to the relatively well-known mechanisms of therapeutic agents. The most widely considered neurodevelopmental hypothesis of schizophrenia integrates environmental influences and causative genes. The dopamine hypothesis of schizophrenia is based on the fact that all common treatments involve antidopaminergic mechanisms and genes such as DRD2, DRD3, DARPP-32, BDNF or COMT are closely related to dopaminergic system functioning. The glutamatergic hypothesis of schizophrenia lead recently to a first successful mGlu2/3 receptor agonistic drug and is underpinned by significant findings in genes regulating the glutamatergic system (SLC1A6, SLC1A2 GRIN1, GRIN2A, GRIA1, NRG1, ErbB4, DTNBP1, DAAO, G72/30, GRM3). Correspondingly, GABA has been proposed to modulate the pathophysiology of the disease which is represented by the involvement of genes like GABRA1, GABRP, GABRA6 and Reelin. Moreover, several genes implicating immune, signaling and networking deficits have been reported to be involved in the disease, i.e. DISC1, RGS4, PRODH, DGCR6, ZDHHC8, DGCR2, Akt, CREB, IL-1B, IL-1RN, IL-10, IL-1B. However, molecular findings suggest that a complex interplay between receptors, kinases, proteins and hormones is involved in schizophrenia. In a unifying hypothesis, different cascades merge into another that ultimately lead to the development of symptoms adherent to schizophrenic disorders.     

Neural mechanisms of hyperalgesia.

Hyperalgesia, or enhanced sensitivity to pain, is a symptom often associated with inflammation, nerve injury and various diseases. Although hyperalgesia appears to be mediated by sensitization of peripheral and central pain-signalling neurons, underlying mechanisms of sensitization are not well understood. Recent contributions to our knowledge of the mechanisms underlying hyperalgesia and sensitization are reviewed.