Neurophysiological Substrates Research Articles

Brain mechanism of Stroop interference effect in Chinese characters

Event-related brain potentials were measured when 11 healthy Chinese subjects finished Chinese Characters Stroop tasks. The behavioral data showed that the Stroop task yielded a robust Stroop interference effect as indexed by longer RT for incongruent than congruent color words. Scalp ERP analysis revealed the neurophysiological substrate of the interference effect: a greater negativity in the incongruent as compared to the congruent was found between 350 and 550 ms poststimulus over midline fronto-central scalp regions. Dipole source analysis (BESA software) of the difference wave (incongruent–congruent) indicated that a generator localized in prefrontal cortex (PFC) contributed to this effect, possibly related to conflict processing and response selection. The results provided electrophysiologic evidences of the brain and cognitive mechanism of Stroop interference effect in Chinese characters and suggested that the difference between Chinese characters and English words had influence on temporal patterns of the Stroop interference effect.

Treatment of drug-induced stereotypy.

One adult of a minority ethnicity, who met criteria for amphetamine-induced psychosis in remission, received treatment for an amphetamine-induced stereotypic behavior. His stereotypic behavior was treated with habit reversal training (HRT), and the treatment's effects were assessed using direct observation procedures. As a result of a two hour intervention, his stereotypic behavior was reduced to near zero levels, and maintained at four month follow-up. Key words: amphetamine, stereotypic behavior, treatment, habit reversal. ********** Amphetamines are quickly becoming one of the most commonly used and manufactured illicit drugs in the world. According to a United Nations report, over 35 million people regularly use amphetamine, compared to the 15 million who regularly use cocaine and the 10 million who use heroin (United Nations Office for Drug Control and Crime Prevention, 2000). Methamphetamine, a derivative of amphetamine, is also one of the fastest growing substance abuse problems in the United States (Yacoubian & Peters, 2004). Once considered largely a concern on the West Coast (e.g., Rawson, Anglin, & Ling, 2002), methamphetamine is becoming much more common in the midwest (Yacoubain & Peters, 2004). Methamphetamine is not only a problem in metropolitan areas; its usage is equally, if not more, common in rural areas (Leukefeld et al., 2002). The increase is due at least in part to the fact that methamphetamine is relatively easy to manufacture and can be created from ingredients that can be purchased legally. Additionally, the effects of methamphetamine last up to 10 to 12 hours, and typical use of methamphetamine costs only about 25% as much as typical cocaine use (Rawson et al., 2000). It is also easy to obtain; the U.S. Department of Justice statistics show that from 1990 to 1996, 64% of high school juniors and seniors reported that they could easily obtain methamphetamine. Like any narcotic, there are both direct effects of the substance and side effects. The direct effects of methamphetamine include increased alertness and energy, elevated self-confidence, and a sense of well-being. The adverse side-effects of prolonged methamphetamine use can include paranoia, slurred speech, motor instability, violent behaviors (Hall, McPherson Twemlow, & Yudko, 2003), psychosis (Lin, Ball, Hsiao, Chiang, Ree, & Chen, 2004), and stereotypic behaviors such as purposeless physical activity, tremors, muscle tics, bruxism (teeth grinding), and athetosis (strange motor movements). This relation between amphetamine use and stereotypic behaviors is well documented in the nonhuman literature (e.g., Canales & Graybiel, 2000, Balsara, Jadhav, Muley, & Chandorkar, 1979). The motor-activating effects of amphetamine in rats is often used for investigating the neurophysiological substrates in human stimulant abuse (Canales, Gilmour, & Iversen, 2000). Rats' behaviors will become increasingly focused and repetitive with increased dosages of amphetamine (Seiden, Sabol, & Ricaurte, 1993). This change in the rats' behavior has been directly liked to changes in the basal ganglia (Canales & Graybiel, 2000). Stereotypic behaviors in rats can be introduced by dopaminergic stimulation of the striatum and can be abolished by intrastriatal blockage of dopaminergic transmission (Arnt 1985; Fibiger, Fibiger & Zis, 1973; Creese & Iverson, 1972). This would seemingly suggest a medically-based intervention for substance-induced stereotypic behaviors; but research is beginning to show that environmentally-based interventions are effective at changing behavior that was the result of brain damage, while demonstrating reliable changes in brain physiology (Latsch, Thulborn, Krisky, Shobat, & Sweeney, 2004). Thus, stereotypic behaviors that are amphetamine-induced may be treatable through environmental manipulations. To date there are no published accounts of the treatment of drug-induced stereotypic behaviors, but there are environmentally based treatment options. …

The Binding Problem in Presence Research

An important contributor to the feeling of being present is the unity of one's perceptual experience. That is, the constellation of sensorial cues in a virtual environment must be in accord with some basic rules which, in the real world, govern the relationship between sensory events. A similar and long standing problem in neuroscience is how is it that the temporally and spatially segregated activity in neuronal ensembles is reassembled in order to generate a seamless conscious experience. This issue, which was first addressed by the Gestalt psychologists, is commonly referred to as the binding problem. In this paper we will discuss how the problem of binding is related to the problem of presence, and how the study of the neurophysiological substrates subserving this process may lead to an understanding of contextual relationships critical to generating presence in virtual environments.

Respiratory evoked potentials and occlusion elicited sympathetic skin response

Introduction. – Neurophysiological study of respiratory structures usually relies upon diaphragm electromyography and phrenic nerve conduction study, which do not assess the afferent sensory pathways. Objective. – To assess the feasibility of respiratory evoked potentials (REPs) and sympathetic skin responses (SSRs) elicited by inspiratory occlusion. Methods. – REPs and SSRs were studied in 12 healthy adults. REPs were elicited by inspiratory occlusions triggered by the physician within 1 s after the onset of a respiratory effort. They were recorded from C3, C4 and Cz needle electrodes (referenced to Fz). Each individual trial consisted of two superimposed 30-sweep averaged responses to inspiratory occlusions. SSRs were recorded from surface electrodes placed on the subject’s hand and elicited by similar inspiratory occlusions. Results. – Reproducible REPs and SSRs were obtained in all subjects. Mean latencies of initial P1 and N1 cortical responses were 41 and 72 ms, respectively. SSRs were similar to those usually elicited by peripheral nerve electrical stimulation. Conclusion. – Brief occlusion of inspiration induces cortical and sympathetic activation, both are easily recordable. Since REPs are considered to be the neurophysiological substrate of certain types of respiratory sensations and are altered in different chronic respiratory diseases, they, in addition to SSR, represent attractive new techniques that may provide better understanding of respiratory dysfunction.

Responses of V1 Neurons to Two-Dimensional Hermite Functions

Neurons in primary visual cortex are widely considered to be oriented filters or energy detectors that perform one-dimensional feature analysis. The main deviations from this picture are generally thought to include gain controls and modulatory influences. Here we investigate receptive field (RF) properties of single neurons with localized two-dimensional stimuli, the two-dimensional Hermite functions (TDHs). TDHs can be grouped into distinct complete orthonormal bases that are matched in contrast energy, spatial extent, and spatial frequency content but differ in two-dimensional form, and thus can be used to probe spatially specific nonlinearities. Here we use two such bases: Cartesian TDHs, which resemble vignetted gratings and checkerboards, and polar TDHs, which resemble vignetted annuli and dartboards. Of 63 isolated units, 51 responded to TDH stimuli. In 37/51 units, we found significant differences in overall response size (21/51) or apparent RF shape (28/51) that depended on which basis set was used. Because of the properties of the TDH stimuli, these findings are inconsistent with simple feedforward nonlinearities and with many variants of energy models. Rather, they imply the presence of nonlinearities that are not local in either space or spatial frequency. Units showing these differences were present to a similar degree in cat and monkey, in simple and complex cells, and in supragranular, infragranular, and granular layers. We thus find a widely distributed neurophysiological substrate for two-dimensional spatial analysis at the earliest stages of cortical processing. Moreover, the population pattern of tuning to TDH functions suggests that V1 neurons sample not only orientations, but a larger space of two-dimensional form, in an even-handed manner.

Behavior of the Position Vestibular Pause (PVP) Interneurons of the Vestibuloocular Reflex During Head-Free Gaze Shifts in the Monkey

Most behavioral studies indicate that the efficacy (gain) of the vestibuloocular reflex (VOR) in primates is modulated during the voluntary head movements that accompany large shifts in the direction of gaze. However, the timing and degree of this modulation is the subject of some debate. The neurophysiological substrate for this apparent gain reduction has been sought in the behavior of the type I position vestibular pause (PVP) neuron, a well-known type of interneuron in the direct VOR pathway. With the head fixed, PVPs increase their firing rates with contraversive eye position and with ipsiversive passive head rotation and also cease firing (pause) for the duration of ipsiversive saccades. During head-free ipsiversive gaze shifts, the eyes and head move in the same direction. If the vestibular signal carried by PVPs provides the primary drive for the VOR, the vestibular signal should be present during ipsiversive gaze shifts to the degree that the VOR is present. Of 25 type I PVPs recorded, 21 ceased their discharge for the entire duration of the rapid, eye-saccade component of an ipsiversive gaze shift. The resumption of activity occurred, on average, 13 ms after the end of the saccade. These results suggest that the activity of the vast majority of PVP neurons do not reflect the state of the VOR, but rather PVPs are completely eliminated from participation in the reflex during head-free gaze movements. We conclude that if any modulation of the VOR does exist, it must occur through other, probably longer-latency, pathways.

Physiological and pathological oscillatory networks in the human motor system

Human brain functions are heavily contingent on neural interactions both at the single neuron and the neural population or system level. Accumulating evidence from neurophysiological studies strongly suggests that coupling of oscillatory neural activity provides an important mechanism to establish neural interactions. With the availability of whole-head magnetoencephalography (MEG) macroscopic oscillatory activity can be measured non-invasively from the human brain with high temporal and spatial resolution. To localise, quantify and map oscillatory activity and interactions onto individual brain anatomy we have developed the ‘dynamic imaging of coherent sources’ (DICS) method which allows to identify and analyse cerebral oscillatory networks from MEG recordings. Using this approach we have characterized physiological and pathological oscillatory networks in the human sensorimotor system. Coherent 8 Hz oscillations emerge from a cerebello-thalamo-premotor-motor cortical network and exert an 8 Hz oscillatory drive on the spinal motor neurons which can be observed as a physiological tremulousness of the movement termed movement discontinuities. This network represents the neurophysiological substrate of a discrete mode of motor control. In parkinsonian resting tremor we have identified an extensive cerebral network consisting of primary motor and lateral premotor cortex, supplementary motor cortex, thalamus/basal ganglia, posterior parietal cortex and secondary somatosensory cortex, which are entrained in the tremor or twice the tremor rhythm. This low frequency entrapment of motor areas likely plays an important role in the pathophysiology of parkinsonian motor symptoms. Finally, studies on patients with postural tremor in hepatic encephalopathy revealed that this type of tremor results from a pathologically slow thalamocortical and cortico-muscular coupling during isometric hold tasks. In conclusion, the analysis of oscillatory cerebral networks provides new insights into physiological mechanisms of motor control and pathophysiological mechanisms of tremor disorders.

EEG and intelligence: Relations between EEG coherence, EEG phase delay and power

Objective There are two inter-related categories of EEG measurement: 1, EEG currents or power and; 2, EEG network properties such as coherence and phase delays. The purpose of this study was to compare the ability of these two different categories of EEG measurement to predict performance on the Weschler Intelligence test (WISC-R). Methods Resting eyes closed EEG was recorded from 19 scalp locations with a linked ears reference from 442 subjects aged 5–52 years. The Weschler Intelligence test was administered to the same subjects but not while the EEG was recorded. Subjects were divided into high IQ (≥120) and low IQ (≤90) groups. EEG variables at P<.05 were entered into a factor analysis and then the single highest loading variable on each factor was entered into a discriminant analysis where groups were high IQ vs. low.Q. Results Discriminant analysis of high vs. low IQ was 92.81–97.14% accurate. Discriminant scores of intermediate IQ subjects (i.e. 90<IQ<120) were intermediate between the high and low IQ groups. Linear regression predictions of IQ significantly correlated with the discriminant scores ( r=0.818–0.825, P<10 −6). The ranking of effect size was EEG phase>EEG coherence>EEG amplitude asymmetry>absolute power>relative power and power ratios. The strongest correlations to IQ were short EEG phase delays in the frontal lobes and long phase delays in the posterior cortical regions, reduced coherence and increased absolute power. Conclusions The findings are consistent with increased neural efficiency and increased brain complexity as positively related to intelligence, and with frontal lobe synchronization of neural resources as a significant contributing factor to EEG and intelligence correlations. Significance Quantitative EEG predictions of intelligence provide medium to strong effect size estimates of cognitive functioning while simultaneously revealing a deeper understanding of the neurophysiological substrates of intelligence.

Intracortical Origins of Interocular Suppression in the Visual Cortex

The response of neurons in the primary visual cortex to an optimally oriented grating is usually suppressed quite dramatically when a second grating of, for example, orthogonal orientation is superimposed. Such "cross-orientation suppression" has been implicated in the generation of cortical orientation selectivity and local response normalization. Until recently, little experimental evidence was available concerning the neurophysiological substrate of this phenomenon, although an involvement of intracortical inhibition was commonly assumed. However, Freeman et al. (2002) proposed that cortical cross-orientation suppression is caused by suppression in the thalamus and depression at geniculocortical synapses. Here, we examine a dichoptic form of cross-orientation suppression, termed interocular suppression and thought to be involved in binocular rivalry (Sengpiel et al., 1995a). We show that its dependency on the drift rate of the suppressing stimulus is consistent with a cortical origin; unlike monocular cross-orientation suppression, it cannot be evoked by very fast-moving stimuli. Moreover, we find that previous adaptation to the orthogonal stimulus essentially eliminates interocular suppression. Because adaptation is a cortical phenomenon, this result also argues in favor of a cortical locus of suppression, again unlike monocular cross-orientation suppression, which is not affected by adaptation to the suppressor (Freeman et al., 2002). Finally, interocular suppression is greatly reduced in the presence of the GABA antagonist bicuculline. Together, our study demonstrates that interocular suppression is substantially different from monocular cross-orientation suppression and is mediated by inhibitory circuitry within the visual cortex.

Recollection of vivid memories after perirhinal region stimulations: synchronization in the theta range of spatially distributed brain areas

Electrical stimulation of the temporal cortex in patients with epilepsy sometimes elicits experiential phenomena such as recollection of vivid memories. The neurophysiological substrate of such phenomena is poorly understood. Furthermore, the relation between the site of stimulation and the type of memory elicited has only recently started to be investigated. We investigated these issues in patient FGA who had intracerebral electrodes stereotaxically implanted in the right temporal lobe for investigation of drug-resistant epilepsy. We report the results of electrical stimulations of the perirhinal region. Two stimulations elicited experiential phenomena consisting of visual memories that belonged to FGA's past, but which were not related to any particular episode. These visual memories consisted of objects or of details of objects. These two stimulations were contrasted with other stimulations in the same subhippocampal region. Cross-correlation analysis of the depth-EEG signals filtered in frequency sub-bands revealed that experiential phenomena occurred only when the various brain structures involved in the after-discharge were synchronized in the theta range. These structures included the perirhinal region, the hippocampus, other limbic structures as well as a primary visual area. Our results suggest that recollection of vivid memory after electric stimulation of the cortex may rely on wide networks of brain areas that transiently synchronize. These results also highlight the role of the perirhinal region in human memory. Experiential phenomena are rarely obtained after brain stimulation. Replication of these results is thus required due to the small number of observations reported.

Neurophysiologic Correlates of Side Effects in Normal Subjects Randomized to Venlafaxine or Placebo

Adverse events reported in the context of medication administration may be due to pharmacodynamic and/or nonpharmacodynamic effects (eg, nocebo phenomena). Neurophysiological substrates of side effects may be examined in placebo-controlled antidepressant treatment trials. We explored the relationship between side effects and regional neurophysiologic changes in normal subjects receiving a 1-week placebo lead-in followed by 4 weeks randomized treatment with placebo (n = 15) or venlafaxine IR (n = 17). Quantitative electroencephalographic (QEEG) cordance measures were obtained before and during treatment, and side effects were assessed weekly using semistructured interviews. Side effect burden, characterized as the mean number of side effects per postrandomization visit, correlated significantly with neurophysiologic changes in the antidepressant group but not the placebo group. Medication group side effects were negatively correlated with changes in prefrontal cordance at end of placebo lead-in (r = -0.67, p < 0.003), at 2 weeks (r = -0.77, p < 0.002), and at 4 weeks (r = -0.77, p < 0.004) post randomization. After controlling for the prefrontal change at the end of placebo lead-in, postrandomization brain changes did not further explain side effect burden. Changes in prefrontal brain function associated with later antidepressant side effects were observed during placebo lead-in-prior to the administration of medication. Prefrontal brain function during brief placebo administration may help explain susceptibility to the development of antidepressant side effects. Results of these exploratory hypothesis-generating analyses should be considered tentative until replicated.

The effect of directional compatibility on the response latencies of ocular and manual movements

Visuomotor coordination is essential for the successful performance of everyday activities, and it could be affected by the directional compatibility between ocular and manual movements. Many tasks, such as driving or operating devices in the workplace, require a variety of coordination patterns with different levels of compatibility between the eyes and the hand. For example, the movement of the eyes and the arm can be coupled when both effectors point towards the same direction whereas in other tasks the movement of the eyes and the arm can be dissociated, for instance when a peripheral object is foveated while a button press response is executed concurrently. The objective of this study was to examine the latency of ocular and manual movements in tasks characterized by variations in directional compatibility. Four tasks were used to manipulate compatibility: 1. point and look at a peripheral stimulus (POINT AND LOOK)--high directional compatibility; 2. point to a peripheral stimulus while fixating in the center (POINT AND FIXATE)--low directional compatibility; 3. press a button while looking at a peripheral stimulus (PRESS AND LOOK)--low directional compatibility; and 4. press a button while fixating in the center (PRESS AND FIXATE)--no directional motor requirement. We hypothesized that the latency of (1) manual and (2) ocular responses would be faster in the task with high directional compatibility compared with the tasks with low compatibility or the task with no directional motor component. Ten healthy participants executed pointing and pressing movements with and without concurrent eye movement to randomly presented visual stimuli. In agreement with the first hypothesis, results showed that in a task with high directional compatibility, manual responses were initiated significantly faster when compared with the tasks with low compatibility or a task with no directional motor component: 1. pointing while looking was initiated 22 ms faster on average than pointing while fixating; 2. pointing while looking was initiated 91 ms faster than pressing accompanied by an eye movement; and 3. pointing while looking was initiated 102 ms faster than pressing while fixating. The second hypothesis was partially supported by data which showed that eye movements directed toward peripheral stimuli were initiated significantly more slowly (30 ms on average) when accompanied by pressing in comparison with the latency of eye movements in the high-compatibility task. In contrast with the hypothesis, eye movements that were accompanied by pointing were not initiated faster than those in a task which required looking without pointing. In summary, these data suggest that directional compatibility is an important aspect of motor control. The effects of directional compatibility are discussed in a conceptual framework that considers the neurophysiological substrates that might be involved in mediating these effects.

An integrative approach to the neurophysiological substrates of social withdrawal and aggression.

An integrative model of the neurophysiology of aggression and social withdrawal is proposed. A detailed overview of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis is presented first, because we consider it to be a critical system that interacts with a variety of physiological processes to modulate affect-related behaviors. This detailed analysis of the LHPA axis is then used to clarify the research literature that links aggression and social withdrawal to LHPA functioning. We then review the role of amygdala and prefrontal cortex functioning in modulating aggression and social withdrawal. Particular attention is paid to how the amygdala and the prefrontal cortex interact with the LHPA system and the environment to produce specific behavioral tendencies throughout development. A brief overview of the implied methodological and theoretical model is provided. We explain how a detailed understanding of specific physiological processes is essential in order to develop appropriate research protocols. In addition, we suggest that future research should focus on the mapping of distinct integrative biosocial profiles that are related to specific behaviors during different developmental stages.

Can literacy change brain anatomy?

Several studies have postulated that education and/or literacy may not only protect against the effects of biological ageing (Albert et al., 1995; Christensen & Henderson, 1991; Orrell & Sahakian, 1995), but also against the clinical manifestation of cerebral neuropathology (Katzman, 1993; Stern, 2002; Stern, Gurland, Tatemichi, Tang, Wilder, & Mayeux, 1994; Zhang et al., 1990). In clinical neuropsychology, much debate has centred on whether the brain is more likely to degenerate as a result of overuse or underuse; while some epidemiological studies have suggested that active engagement in intellectual, social, and physical activities may delay the cognitive deterioration associated with normal ageing (Scarmeas, Levy, Tang, Manly, & Stern, 2001), other studies have emphasized that the protective effect of education is not always observed but depends upon the specific cognitive ability that is measured (Ardila, Ostrosky-Solis, Rosselli, & Gomez, 2000; Ostrosky-Solis, Ardila, Rosselli, Lopez, & Mendoza, 1998). Ostrosky-Solis (2002) points out that protection or age-related decline attenuation in well-educated subjects is highly related to verbal abilities; thus, education and verbal advantage could serve as a means of compensatory strategies, such as using verbal cues to aid recall or encoding visuospatial tasks with language. These are the strategies provided by formal education. The use of these strategies could mask otherwise similar rates of biological ageing among different educational groups, and this advantage, coupled with the effects of several important variables such as good health, appropriate occupation, and active engagement with the surrounding environment, could explain why cognitive stimulation can provide some moderating influence on the complex changes in cognitive performance associated with ageing. It has also been reported that Alzheimer’s disease not only has a later onset but that it is less severe in highly educated people (Katzman, 1993; Stern et al., 1994). This association of high education with late age of onset of dementia has been considered as an evidence of cognitive and/or brain reserve (Katzman, 1993; Mortimer, 1988; Satz, 1993; Stern, 2002). The articles presented in this Special Issue analyse the impact of literacy on the anatomic and functional organization of the adult brain. Cognitive neuroimaging studies, event-related potentials, neuropsychological data of literate and illiterate subjects, and discussion regarding the origins and evolution of reading and writing are presented. Stern, Scarmeas, and Habeck point out that the cognitive reserve model suggests that variables such as education and IQ are associated with cognitive reserve (CR) and may mediate differential susceptibility to age-related memory changes. They propose two complementary facets to CR: reserve—individual differences in the capacity to perform task—and compensation—the use of alternate brain networks or cognitive processes to cope with brain pathology. However, up to now the neurophysiologic substrate of CR has not been established. Therefore in order to explore the anatomical basis for CR in healthy young and old individuals, they used H215O PET to analyse the relationship between CR and task-related activation during the performance of a nonverbal recognition memory test. The first two studies focused on young subjects, and found either brain areas or brain networks where the amount of increased activation correlated with CR. The third study compared activation patterns of young and elderly individuals and found locations where the relation between activation and CR differed

Prefrontal-cingulate activation during executive control: which comes first?

The Stroop test requires executive control functions, in particular inhibition of a learned routine (in this case, word reading). The spatiotemporal analysis of brain activation during Stroop task execution was performed in 16 healthy subjects using high-density event-related potentials (ERPs) and dipole source modeling (BESA software). Scalp ERP analysis revealed the neurophysiological substrate of the interference effect: first, a greater negativity in the incongruent as compared to the congruent and neutral conditions was found between 350 and 450 ms poststimulus over left frontocentral scalp regions. Source analysis of the difference wave (incongruent–congruent) indicated that a generator localized in left prefrontal cortex (PFC) contributed to this effect. Second, immediately after the first effect, a greater positivity in the incongruent as compared to the congruent and neutral conditions developed between 450 and 550 ms poststimulus over midline frontocentral scalp regions. A generator of this effect was located in right anterior cingulate cortex (ACC). ACC activation seems to follow the activation of PFC with some overlap between the two components. Possible interpretation of this finding is that PFC signals ACC when executive control is required and ACC implements the control.

Neurophysiological factors in human information processing capacity.

What determines how well an individual can manage the complexity of information processing demands when several tasks have to be executed simultaneously? Various theoretical frameworks address the mechanisms of information processing and the changes that take place when processes become automated, and brain regions involved in various types of information processing have been identified, as well as sequences of events in the brain. The neurophysiological substrate of human information processing capacity, i.e. the amount that can be processed simultaneously, is, however, unresolved, as is the basis of inter-individual variability in capacity. Automatization of cognitive functions is known to increase capacity to process additional tasks, but behavioural indices of automatization are poor predictors of processing capacity in individuals. Automatization also leads to a decline of brain activity in the working memory system. In this study, we test the hypothesis that processing capacity is closely related to the way that the brain adjusts to practice of a single cognitive task, i.e. to the changes in neuronal activity that accompany automatization as measured with functional MRI (fMRI). Using a task that taxes the working memory system, and is sensitive to automatization, performance improved while activity in the network declined, as expected. The key finding is that the magnitude of automatization-induced reduction of activity in this system was a strong predictor for the ability to perform two different working memory tasks simultaneously (after scanning). It explained 60% of the variation in information processing capacity across individuals. In contrast, the behavioural measures of automatization did not predict this. We postulate that automatization involves at least two partially independent neurophysiological mechanisms, i.e. (i) streamlining of neuronal communication which improves performance on a single task; and (ii) functional trimming of neuronal ensembles which enhances the capacity to accommodate processing of additional tasks, potentially by facilitating rapid switching of instruction sets or contexts. Finally, this study shows that fMRI can provide information that predicts behavioural output, which is not provided by overt behavioural measures.

When the self represents the other: A new cognitive neuroscience view on psychological identification

There is converging evidence from developmental and cognitive psychology, as well as from neuroscience, to suggest that the self is both special and social, and that self–other interaction is the driving force behind self-development. We review experimental findings which demonstrate that human infants are motivated for social interactions and suggest that the development of an awareness of other minds is rooted in the implicit notion that others are like the self. We then marshal evidence from functional neuroimaging explorations of the neurophysiological substrate of shared representations between the self and others, using various ecological paradigms such as mentally representing one’s own actions versus others’ actions, watching the actions executed by others, imitating the others’ actions versus being imitated by others. We suggest that within this shared neural network the inferior parietal cortex and the prefrontal cortex in the right hemisphere play a special role in the essential ability to distinguish the self from others, and in the way the self represents the other. Interestingly, the right hemisphere develops its functions earlier than the left.

Multiple levels of representation of reaching in the parieto-frontal network.

In daily life, hand and eye movements occur in different contexts. Hand movements can be made to a visual target shortly after its presentation, or after a longer delay; alternatively, they can be made to a memorized target location. In both instances, the hand can move in a visually structured scene under normal illumination, which allows visual monitoring of its trajectory, or in darkness. Across these conditions, movement can be directed to points in space already foveated, or to extrafoveal ones, thus requiring different forms of eye-hand coordination. The ability to adapt to these different contexts by providing successful answers to their demands probably resides in the high degree of flexibility of the operations that govern cognitive visuomotor behavior. The neurophysiological substrates of these processes include, among others, the context-dependent nature of neural activity, and a transitory, or task-dependent, affiliation of neurons to the assemblies underlying different forms of sensorimotor behavior. Moreover, the ability to make independent or combined eye and hand movements in the appropriate order and time sequence must reside in a process that encodes retinal-, eye- and hand-related inputs in a spatially congruent fashion. This process, in fact, requires exact knowledge of where the eye and the hand are at any given time, although we have no or little conscious experience of where they stay at any instant. How this information is reflected in the activity of cortical neurons remains a central question to understanding the mechanisms underlying the planning of eye-hand movement in the cerebral cortex. In the last 10 years, psychophysical analyses in humans, as well as neurophysiological studies in monkeys, have provided new insights on the mechanisms of different forms of oculo-manual actions. These studies have also offered preliminary hints as to the cortical substrates of eye-hand coordination. In this review, we will highlight some of the results obtained as well as some of the questions raised, focusing on the role of eye- and hand-tuning signals in cortical neural activity. This choice rests on the crucial role this information exerts in the specification of movement, and coordinate transformation.

P.1.245 Effects of an educational compliance enhancement programme and therapeutic drug monitoring on treatment adherence and treatment response in depression

We summarize clinical and polysomnographic findings in support of the existence of a broad and prevalent spectrum of less than syndromal or subthreshold depressive conditions that constitute subaffective disorders. Many of these conditions were previously subsumed under such rubrics as `neurotic,' `characterological,' and `existential' depressions. Prospective follow-up studies of neurotic depressions (defined by a predominance of the psychological features of, in most instances, less than syndromal depression) have demonstrated their transformation into moderate to melancholic or psychotic depressive, and even bipolar, disorders. Many characterological depressives (outpatients with early insidious onset and fluctuating chronicity of subthreshold manifestations falling short of full syndromal depression), were shown to have shortened REM latency, increased REM%, redistribution of REM to the first part of the night, classic diurnality, high rates of family history for mood disorders, positive response to antidepressants and sleep deprivation, and prospective follow-up course leading to major affective episodes. Shortened REM latency and related sleep neurophysiological disturbances have also been reported to characterize so-called `borderline' personality disorder even when examined in the absence of concomitant major depression.Finally, among primary care referrals to a sleep disorders center, short REM latency was found in a large number of patients without subjective mood change but with somatic manifestations of depression (meeting Probable Feighner Depression and/or lesser subacute manifestations). Rather than being incidental, the REM disturbances in the foregoing studies appear consistently on consecutive nights of polysomnography in the subthreshold affective group; this was not the case for patients with non-affective personality and anxiety disorders. The findings overall tend to support a common neurophysiological substrate for subthreshold and melancholic depressions and, interpreted in the context of clinical observations, family history and follow-up course, uphold the validity of dysthymic, intermittent and subsydromal depressions.

Unaltered respiratory-related evoked potentials after acute diaphragm dysfunction in humans

Respiratory muscles play an important role in the origin of respiratory sensations. Data dissecting the role of the diaphragm and other inspiratory muscles are scarce. This study aimed to determine the impact of diaphragm dysfunction following inspiratory resistive loading on respiratory-related evoked potentials considered as a neurophysiological substrate of certain types of respiratory sensations. Altogether, nine subjects aged 25-50 yrs (six females) participated in the study. Transdiaphragmatic pressure output of cervical magnetic stimulation (with subdivision in oesophageal and gastric component), and respiratory-related evoked potentials (C3 and C4 derivations in the international 10-20 system) following mid-inspiratory occlusions were studied before and after an inspiratory-resistive loading challenge. Predominant diaphragm dysfunction was observed in seven subjects (average 28% reduction in transdiaphragmatic pressure, from 27.25-19.91 cmH2O, with increased oesophageal-to-gastric pressure ratio). The latencies and amplitudes of all the components of the respiratory-related evoked potentials were unchanged. The study concluded that predominant diaphragm fatigue does not affect respiratory-related evoked potentials.