Time pressure modulates electrophysiological correlates of early visual processing

Background

Reactions to sensory events sometimes require quick responses whereas at other times they require a high degree of accuracy–usually resulting in slower responses. It is important to understand whether visual processing under different response speed requirements employs different neural mechanisms.

Methodology/Principal Findings

We asked participants to classify visual patterns with different levels of detail as real-world or non-sense objects. In one condition, participants were to respond immediately, whereas in the other they responded after a delay of 1 second. As expected, participants performed more accurately in delayed response trials. This effect was pronounced for stimuli with a high level of detail. These behavioral effects were accompanied by modulations of stimulus related EEG gamma oscillations which are an electrophysiological correlate of early visual processing. In trials requiring speeded responses, early stimulus-locked oscillations discriminated real-world and non-sense objects irrespective of the level of detail. For stimuli with a higher level of detail, oscillatory power in a later time window discriminated real-world and non-sense objects irrespective of response speed requirements.

Conclusions/Significance

Thus, it seems plausible to assume that different response speed requirements trigger different dynamics of processing.     

EEG correlates of the change in information processing strategy in visual imagery

Cnanger of the spatial organization of biopotentials (spatial synchronization and disorder, spectral power and coherence) were analyzed during mental creating of visual images from two simple elements: the angle the oblique line. With the transition from the first to the fourth task, the total number of used elements increased from the number suitable for simultaneous presentation and conscious processing (less than 7 +/- 2) to a much higher number. Changes in the characteristics of the spatial organization of biopotentials associated with the increase in the number of the elements can be explained by a change in the information processing strategy, transformation of information processing strategy, i.e. the transition from the left-hemispheric successive (conscious) analyses to the right-hemispheric simultaneous (unconscious) processing. It was shown that this change in the information processing strategy was accompanied by an increase in the index of spatial disorder sensitive to complicated nonlinear processes. Subjects were divided in two groups with different forms of the reorganization of interhemispheric and fronto-occipital relationships of biopotentials. These data are interpreted in terms of different involvement of the unconscious intellectual processes of different layers (subconsciousness and superconsciousness) in the change in information processing strategy.     

Interindividual differences in the circadian hematologic time structure of cancer patients

The complete hematologic blood cell count of 11 patients with advanced cancer were determined on 14 occasions, every 4 hr over 36-48 hr. Oral temperature was also measured at the same times as blood sampling. Five patients had breast cancer, five had ovarian cancer and one a leiomyosarcoma. Circadian rhythms were detected by the cosinor method for seven hematologic variables (red blood cells, hemoglobin, hematocrit, white blood cells, neutrophils, lymphocytes, platelets) and for oral temperature in the whole group of patients. All acrophases were located between 1300 and 1700 hr, except for lymphocytes (2100 hr). A rhythm with a period of 8 hr was validated for lymphocytes and monocytes. Validated or estimated amplitudes and acrophases were closely similar in both breast and ovarian cancer subgroups. Individual cosinor analyses documented large differences from patient to patient, which were accounted for by differences in performance status. Thus, subjects with poor performance status and rapidly progressive disease had very few validated rhythms as compared to those patients with good performance status. As a result a statistically significant correlation was found between the number of validated hematologic circadian rhythms and the performance status (r = -0.88; P less than 0.01).     

Functional-anatomic correlates of individual differences in memory

Memory abilities differ greatly across individuals. To explore a source of these differences, we characterized the varied strategies people adopt during unconstrained encoding. Participants intentionally encoded object pairs during functional MRI. Principal components analysis applied to a strategy questionnaire revealed that participants variably used four main strategies to aid learning. Individuals' use of verbal elaboration and visual inspection strategies independently correlated with their memory performance. Verbal elaboration correlated with activity in a network of regions that included prefrontal regions associated with controlled verbal processing, while visual inspection correlated with activity in a network of regions that included an extrastriate region associated with object processing. Activity in regions associated with use of these strategies was also correlated with memory performance. This study reveals functional-anatomic correlates of verbal and perceptual strategies that are variably used by individuals during encoding. These strategies engage distinct brain regions and may separately influence memory performance.     

Interindividual differences in thermal comfort and the responses to skin cooling in young women

The present study aims to understand the effects of interindividual differences in thermal comfort on the relationship between the preferred temperature and the thermoregulatory responses to ambient cooling. Thirteen young women subjects chose the preferred ambient temperature (preferred T_a) in a climate chamber and were categorized into the H group (preferring ≥29 °C; n=6) and the M group (preferring <29 °C; n=7). The H group preferred warmer sensations than the M group (P<0.05) and the average of preferred T_a was 27.6 °C and 30.2 °C in the M group and H group, respectively. Then all subjects were exposed to temperature variations in the climate chamber. During T_a variations from 33 °C to 25 °C, the H group felt colder than the M group, although no difference was noted in the T_sk (mean skin temperature) and T_s-hand between the 2 groups. From the view of the relationship between the T_sk and thermal sensation, although the thermal sensitivity to the T_sk was almost similar in the H and M groups, the H group might have lower threshold to decreasing T_a than the M group.     

Interindividual differences in leg muscle mass and pyruvate kinase activity correlate with interindividual differences in jumping performance of Hyla multilineata

Frog jumping is an excellent model system for examining the structural basis of interindividual variation in burst locomotor performance. Some possible factors that affect jump performance, such as total body size, hindlimb length, muscle mass, and muscle mechanical and biochemical properties, were analysed at the interindividual (intraspecies) level in the tree frog Hyla multilineata. The aim of this study was to determine which of these physiological and anatomical variables both vary between individuals and are correlated with interindividual variation in jump performance. The model produced via stepwise linear regression analysis of absolute data suggested that 62% of the interindividual variation in maximum jump distance could be explained by a combination of interindividual variation in absolute plantaris muscle mass, total hindlimb muscle mass (excluding plantaris muscle), and pyruvate kinase activity. When body length effects were removed, multiple regression indicated that the same independent variables explained 43% of the residual interindividual variation in jump distance. This suggests that individuals with relatively large jumping muscles and high pyruvate kinase activity for their body size achieved comparatively large maximal jump distances for their body size.     

Individual differences in emotion processing

Recent functional brain imaging studies of the neurobiology of emotion have investigated how individual differences among subjects modulate neural responses during emotion processing. Differences in personality, dispositional affect, biological sex, and genotype can all substantially modulate the neural bases of emotion processing in prefrontal, limbic, and other brain regions, across a variety of domains including emotional reactions, emotional memory, and emotion perception. Analysis of individual differences provides a new window into the neurobiology of emotion processing that complements traditional approaches.     

Short-term cardiovascular responses to repeated exposure to intermittent noise. Interindividual differences

Human subjects were exposed for two (or three) sessions to the same runs of 103 dB (A) pink noise-steps alternating with 40 dB (A) low level pink noise. From one session to the following their cardiovascular responses seem to achieve an adjustment. Differences between them depend on two features: (1) some of them achieve a negative feedback reaction from the second exposure, when in others such a reaction is delayed until the third exposure; (2) parallelism or opposition between evolutions of heart rate and arterial blood pressure respectively.     

Neural correlates of individual differences in circadian behaviour

Daily rhythms in mammals are controlled by the circadian system, which is a collection of biological clocks regulated by a central pacemaker within the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Changes in SCN function have pronounced consequences for behaviour and physiology; however, few studies have examined whether individual differences in circadian behaviour reflect changes in SCN function. Here, PERIOD2::LUCIFERASE mice were exposed to a behavioural assay to characterize individual differences in baseline entrainment, rate of re-entrainment and free-running rhythms. SCN slices were then collected for ex vivo bioluminescence imaging to gain insight into how the properties of the SCN clock influence individual differences in behavioural rhythms. First, individual differences in the timing of locomotor activity rhythms were positively correlated with the timing of SCN rhythms. Second, slower adjustment during simulated jetlag was associated with a larger degree of phase heterogeneity among SCN neurons. Collectively, these findings highlight the role of the SCN network in determining individual differences in circadian behaviour. Furthermore, these results reveal novel ways that the network organization of the SCN influences plasticity at the behavioural level, and lend insight into potential interventions designed to modulate the rate of resynchronization during transmeridian travel and shift work.     

Autonomic correlates of individual differences in human intellectual activity

The individual differences in the autonomic support of intellectual activity, including simple and complex sensorimotor reactions, memorization and reproduction (on the screen of the monitor) of visual information, were studied. The rate of performing intellectual computer-aided tests is a relatively steady individual characteristic revealed in different kinds of activity. Students who reached a high speed and accurately performed intellectual visuomotor tasks were characterized by a high lability of autonomic indices, which manifests itself in a change in the absolute values and relationship of heart and respiration rates in accordance with activity stages. These changes were specific for each form of activity and were connected with the results of the tests. Under the initial conditions, these students were characterized by high values of TP and the power of the LF and HF ranges of heart rate variability at a LF/HF ratio close to unity.     

家蚕味觉电生理反应的个体差异

为探讨家蚕Bombyx mori人工饲料饲养发育不齐的生理原因,从同一蚕品种中挑选出对人工饲料摄食性不同的个体,用电生理学方法测定了下颚瘤状体味觉感器对4种代表性物质（蔗糖、肌醇、大豆粉提取物和柠檬酸）的电生理反应。结果表明,栓锥感器Ss-Ⅰ对蔗糖等促食物质的反应以及栓锥感器Ss-Ⅱ对大豆粉提取物等阻食物质的反应,均存在明显的个体差异。在临界浓度下,低摄食性个体的放电脉冲频率显著高于高摄食性个体。说明低摄食性蚕的味觉反应比高摄食性蚕敏感。     

The information processing organisms

In spite of the tremendous progress in recent decades of biological science, many aspects of the behaviour of organisms in general and of humans in particular remain still somewhat obscure. A new approach towards the study of the behaviour of man was presented by Heisenberg when he emphasized that a Cartesian view of nature as an object “out there” is an illusion in so far as “the observer is always part of the formula, the man viewing nature must be figured in, the experimenter into his experiment and the artist in the scene he paints.” (Heisenberg, 1969). The present study is an attempt to make a step forward in this direction by focusing on the ways and means of involvement of the observer which make him an indelible part of the observation. To get a fresh start let us have a look at the physical universe. Although showing an immense variety, all objects, living and non-living, have some characteristics in common. They all obey the physical laws and they all are engaged in perpetual interactions. How do we tell then the difference between living and non-living objects? According to the traditional concept it is the capacity for reproduction that distinguishes living from non-living objects. (Luria et al., 1981). The non-traditional concept presented in this study stresses the way in which objects interact as the crucial point of difference between living and non-living objects. This concept claims that living objects assert themselves as such only when and while interacting in terms of information processing. Under such conditions only, living objects are able to display relative independence of the physical laws, for instance active movement. This display of relative independence is governed by biological laws and defines the behaviour of the living objects as active in principle. All objects who share these characteristics are called living, they behave as wholes assessing themselves as individuals. The definition suggests that they all share the same internal organization which is principally dynamic.     

Ultrastructural and electrophysiological correlates of cell coupling and cytoplasmic fusion during myogenesis in vitro

An electrophysiological monitoring strategy involving iontophoretic application of acetylcholine and intracellular recording has been employed in an investigation of the time course of cell fusion during myogenesis in vitro. Pairs of closely apposed, acetylcholine-sensitive rat or chick myogenic cells were continuously monitored. The onset of high-efficiency electrical coupling between members of such pairs corresponded to the moment at which cytoplasmic continuity was established. Ultrastructural analysis of the serial section record of two rat myotubes, fixed 2–3 min after fusion began, demonstrated the rapid disappearance of surface membranes in the fusion area at an average rate > 1 μm² of membrane per second. Ten pairs of acetylcholine-sensitive cells were also observed to form lower-efficiency electrical connections. Such cells were not fused but were associated via specialized close membrane appositions resembling gap junctions. These membrane appositions apparently persist through the early events of cell fusion, for their remnants were found in recently fused cells. Possible roles of electrical coupling and of these close junctions in the fusion process are considered.     

Adaptive information processing in microtubule networks

Microtubule networks provide a wide range of microskeletal and micromuscular functionalities. Evidence from a number of directions suggests that they can also serve as a medium for intracellular signaling processing. The model presented here comprises an empirically motivated representation of microtubule growth dynamics, an abstract representation of signal processing, and a feedback learning mechanism that we refer to as adaptive self-stabilization. The growth model mimics the dynamic instability picture of microtubule formation and decomposition, but as modulated by the binding activity of microtubule associated proteins (or MAPs). The signal processing submodel treats each microtubule as a string of linked discrete oscillators capable of propagating signals that are introduced, manipulated, and extracted by bound MAP activity. Adaptive self-stabilization is essentially feedback acting on signal processing capabilities via the growth dynamics. The network is presented with a training set of patterns. If the input-output behavior is satisfactory MAP binding affinity increases, thereby stabilizing the network structure; otherwise the binding affinity decreases, allowing for more structural variation. The results obtained suggest that adaptive capabilities are practically inevitable in microtubule networks, a conclusion strengthened by the fact that the signal processing and growth dynamics mechanisms available in nature are undoubtedly much richer than those represented in the model.     

Microscopic-macroscopic interface in biological information processing

Recent experimental work suggests that chemical messengers associated with the neuron membrane serve as a link between macroscopic and microscopic information processes in the brain. Arguments based on the physical limits of computing, on computational parallelism, and on evolution theory suggest that microphysical computing processes enormously enhance the brain's computing power. A number of models are briefly sketched which illustrate how molecular switching processes could be recruited for useful biological functions. The flow of information between microscopic and macroscopic forms is suggestive of processes which occur in a measuring apparatus, and the implications of this analogy are considered.