Stimulus Area Research Articles

Modulation of an inhibitory jaw reflex by remote noxious stimulation: effects of spatial conditioning factors

In humans, inhibitory jaw reflexes can be depressed by painful stimulation of remote parts of the body. The underlying mechanisms may involve diffuse noxious inhibitory controls (DNIC). Animal experiments have shown that the neurons which may mediate DNIC show spatial encoding (i.e. their responses vary in relation to the size of the body area being stimulated). The aim of this study was to investigate whether the modulation of an inhibitory jaw reflex shows similar spatial dependency. Electromyographic recordings were made in 9 subjects, from a masseter muscle that was activated to a level equivalent to 10% of that obtained during a maximum voluntary contraction. Reflex inhibitions were evoked by electrical stimuli to the upper lip, either alone (controls) or during the application of conditioning stimuli (47 degrees C water) to the fingers, the hand, the half forearm or the whole forearm. Conditioning stimuli applied to the larger but not to the smaller areas resulted in significant modulations of the reflex. There was a significant correlation between stimulus area and reflex magnitude. These results demonstrate a spatial dependency for the modulation of an inhibitory jaw reflex by painful stimuli -- a further parallel with DNIC as studied on single neurons in animals.

Topographic Spatial Summation in Glaucoma

Stimulus luminance (L) and area (A) are related by the equation L x A(k)=constant. The authors evaluated the k value at 66 positions of the central visual field in patients with glaucoma, to modify L and A simultaneously in order to examine advanced glaucomas with a bigger dynamic range. The luminance limitation of a computer screen with automatic photometric control was compensated for by increasing the stimulus area in the range between 0 and 17 dB, using the k topographic values previously calculated on normal subjects. Four initial series of 21, 12, 10, and 10 glaucomas were sequentially examined with the Octopus 311 in which the stimulus size cannot be freely changed during the examination, and with the experimental method (Pulsar-SAP) modifying stimulus sizes to equal the results. k Final estimation was verified in 60 new cases. k values increase progressively with defect deepness. Values higher than those of the normal population with equivalent topographic differences were obtained. Correlation between indices was as follows: MD: r=0.94 (p<0.0001); square root of the loss of variance (sLV): r=0.93 (p<0.0001). Frequency of local defects was similar in both procedures. Average topographic differences between thresholds were usually less than 1 dB. The average threshold difference favored Pulsar-SAP by 0.45 dB at those points where the average threshold of both examinations was less than 18 dB and 0.37 dB where such average was higher than or equal to 18 dB. k value is higher in patients with glaucoma than in normal subjects, although the topographic features are similar. It is feasible to design a scale combining stimulus luminance and sizes to use screens with relative low brightness as surfaces for visual field examination.

Chronic urticaria – which clinical parameters are pathogenetically relevant? A retrospective investigation of 339 patients

Urticaria is a clinical reaction pattern triggered by many factors causing liberation of vasoactive substances such as histamine, prostaglandins and kinins. It presents as transient itching wheals which are either limited to the local stimulus area or more widespread. Urticaria is classified according to its duration into acute (duration > or = 6 weeks) and chronic (duration 6 weeks) forms. Various clinical investigations may be initiated to diagnose the cause. This study critically evaluates the relevance of frequently performed laboratory investigations and searches for infectious foci, as well as the results of physical provocation testing and oral provocation with food additives. The laboratory and clinical data of 339 patients who had been treated for urticaria at the Christian-Albrechts-University in Kiel over a period of four years were collected in a data entry form and statistically evaluated. Nominal values were analyzed by their relative and absolute quantities, quantitative parameters with the help of statistical data such as minimum, maximum, median and 25th and 75th percentiles. Chronic recurrent urticaria was most common, accounting for 52% of cases. Women were affected 1.8 times more often than men. One-third of the patients also had angioedema. The medians of all laboratory parameters evaluated were within normal values. Only rarely were elevated antinuclear antibody titers, abnormal thyroid function tests or active infections such as hepatitis B or borreliosis detected. The search for infectious foci identified tonsillitis or sinusitis in almost 50% of analyzed patients. Positive reactions to physical testing occurred in 30% of patients and in 11% to oral provocation with various food additives. This study of a large patient group stresses the relevance of individually-tailored evaluations in patients affected with urticaria rather than an expensive initial broad diagnostic testing. More specific searches should be based on individual clues.

Dissociable effects of phonetic competition and category typicality in a phonetic categorization task: An fMRI investigation

The current study used fMRI to explore the extent to which neural activation patterns in the processing of speech are driven by the quality of a speech sound as a member of its phonetic category, that is, its category typicality, or by the competition inherent in resolving the category membership of stimuli which are similar to other possible speech sounds. Subjects performed a phonetic categorization task on synthetic stimuli ranging along a voice-onset time continuum from [da] to [ta]. The stimulus set included sounds at the extreme ends of the voicing continuum which were poor phonetic category exemplars, but which were minimally competitive, stimuli near the phonetic category boundary, which were both poor exemplars of their phonetic category and maximally competitive, and stimuli in the middle of the range which were good exemplars of their phonetic category. Results revealed greater activation in bilateral inferior frontal areas for stimuli with the greatest degree of competition, consistent with the view that these areas are involved in selection between competing alternatives. In contrast, greater activation was observed in bilateral superior temporal gyri for the least prototypical phonetic category exemplars, irrespective of competition, consistent with the view that these areas process the acoustic–phonetic details of speech to resolve a token's category membership. Taken together, these results implicate separable neural regions in two different aspects of phonetic categorization.

An electrophysiological study on the interaction between emotional content and spatial frequency of visual stimuli

Previous studies suggest that the magnocellular pathway, a visual processing system that rapidly provides low spatial frequency information to fast-responding structures such as the amygdala, is more involved in the processing of emotional facial expressions than the parvocellular pathway (which conveys all spatial frequencies). The present experiment explored the spatio-temporal characteristics of the spatial frequency modulation of affect-related neural processing, as well as its generalizability to non-facial stimuli. To that aim, the event-related potentials (ERPs) elicited by low-pass filtered (i.e., high spatial frequencies are eliminated) and intact non-facial emotional images were recorded from 31 participants using a 60-electrode array. The earliest significant effect of spatial frequency was observed at 135 ms from stimulus onset: N135 component of the ERPs. In line with previous studies, the origin of N135 was localized at secondary visual areas for low-pass filtered stimuli and at primary areas for intact stimuli. Importantly, this component showed an interaction between spatial frequency and emotional content: within low-pass filtered pictures, negative stimuli elicited the highest N135 amplitudes. By contrast, within intact stimuli, neutral pictures were those eliciting the highest amplitudes. These results suggest that high spatial frequencies are not essential for the initial affect-related processing of visual stimuli, which would mainly rely on low spatial frequency visual information. According to present data, high spatial frequencies would come into play later on.

Exploration of the Psychophysics of a Motion Displacement Hyperacuity Stimulus

To explore the summation properties of a motion-displacement hyperacuity stimulus with respect to stimulus area and luminance, with the goal of applying the results to the development of a motion-displacement test (MDT) for the detection of early glaucoma. A computer-generated line stimulus was presented with displacements randomized between 0 and 40 minutes of arc (min arc). Displacement thresholds (50% seen) were compared for stimuli of equal area but different edge length (orthogonal to the direction of motion) at four retinal locations. Also, MDT thresholds were recorded at five values of Michelson contrast (25%-84%) for each of five line lengths (11-128 min arc) at a single nasal location (-27,3). Frequency-of-seeing (FOS) curves were generated and displacement thresholds and interquartile ranges (IQR, 25%-75% seen) determined by probit analysis. Equivalent displacement thresholds were found for stimuli of equal area but half the edge length. Elevations of thresholds and IQR were demonstrated as line length and contrast were reduced. Equivalent displacement thresholds were also found for stimuli of equivalent energy (stimulus area x [stimulus luminance - background luminance]), in accordance with Ricco's law. There was a linear relationship (slope -0.5) between log MDT threshold and log stimulus energy. Stimulus area, rather than edge length, determined displacement thresholds within the experimental conditions tested. MDT thresholds are linearly related to the square root of the total energy of the stimulus. A new law, the threshold energy-displacement (TED) law, is proposed to apply to MDT summation properties, giving the relationship T = K logE where, T is the MDT threshold, Kis the constant, and E is the stimulus energy.

Synaptically released zinc gates long-term potentiation in fear conditioning pathways

The functional role of releasable Zn2+ in the central nervous system remains unknown. Here we show that zinc transporter 3 (ZnT-3), which maintains a high concentration of Zn2+ in synaptic vesicles and serves as a marker for zinc-containing neurons, is enriched in the lateral nucleus of the amygdala and in the temporal area 3 of the auditory cortex, an area that conveys information about the auditory conditioned stimulus to the lateral nucleus of the amygdala, but not in other conditioned stimulus areas located in the auditory thalamus. Using whole-cell recordings from amygdala slices, we demonstrated that activity-dependent release of chelatable Zn2+ is required for the induction of spike timing-dependent long-term potentiation in cortical input to the amygdala implicated in fear learning. Our data indicate that synaptically released Zn2+ enables long-term potentiation at the cortico-amygdala synapses by depressing feed-forward GABAergic inhibition of principal neurons. This regulatory mechanism, implicating pathway-dependent release of Zn2+, may serve an essential control function in assuring spatial specificity of long-lasting synaptic modifications in the neural circuit of a learned behavior.

Processing of autobiographical memory retrieval cues in borderline personality disorder

Background Affective dysregulation in borderline personality disorder (BPD) in response to both external stimuli and memories has been shown to be associated with functional alterations of limbic and prefrontal brain areas. This study aimed to examine neuronal networks involved in autobiographical memory retrieval using standardized stimuli that gain autobiographical significance by illustrating marked solitary and social situations of human life. Methods Using event-related functional Magnetic Resonance Imaging (fMRI), we examined the processing of pictures from the Thematic Apperception Test (TAT) in 14 BPD patients and 14 controls. Results In both groups, TAT stimuli activated brain areas known to be involved in autobiographical memory retrieval. BPD subjects lacked differential amygdala, orbitofrontal and cingulate activations for TAT versus neutral stimuli. In the TAT condition, compared to controls, BPD subjects displayed increased BOLD responses in the bilateral orbitofrontal and insular regions, in the left anterior cingulate and medial prefrontal cortex, as well as in the parietal and parahippocampal areas, consistent with a more aversive and arousing experience assessed by self-reports. Conclusions Increased BOLD responses during TAT processing in BPD subjects were in line with previously reported changes in anterior cingulate and orbitofrontal cortices, which are known to be involved in memory retrieval. However, BPD subjects displayed hyperactivation in these areas for both TAT and neutral stimuli. The deficit of selective activation of areas involved in autobiographical memory retrieval suggests a general tendency towards a self-referential mode of information processing in BPD, or a failure to switch between emotionally salient and neutral stimuli.

Size matters, but not for everyone: Individual differences for contrast discrimination

It is very well known that contrast detection thresholds improve with the size of a grating-type stimulus, but it is thought that the benefit of size is abolished for contrast discriminations well above threshold [e.g., Legge, G. E., & Foley, J. M. (1980)]. Here we challenge the generality of this view. We performed contrast detection and contrast discrimination for circular patches of sine wave grating as a function of stimulus size. We confirm that sensitivity improves with approximately the fourth-root of stimulus area at detection threshold (a log-log slope of -0.25) but find individual differences (IDs) for the suprathreshold discrimination task. For several observers, performance was largely unaffected by area, but for others performance first improved (by as much as a log-log slope of -0.5) and then reached a plateau. We replicated these different results several times on the same observers. All of these results were described in the context of a recent gain control model of area summation [Meese, T. S. (2004)], extended to accommodate the multiple stimulus sizes used here. In this model, (i) excitation increased with the fourth-root of stimulus area for all observers, and (ii) IDs in the discrimination data were described by IDs in the relation between suppression and area. This means that empirical summation in the contrast discrimination task can be attributed to growth in suppression with stimulus size that does not keep pace with the growth in excitation.

Time-frequency analysis of target detection reveals an early interface between bottom-up and top-down processes in the gamma-band

The early visual gamma-band response is an oscillatory signal evoked approximately 100 ms after stimulation. While some studies have found effects of various cognitive processes on this signal, such effects could not be replicated in other studies. Accordingly, some authors have claimed that evoked gamma-band activity reflects merely sensory functions. To resolve these conflicting positions, we conducted a target detection experiment in which the feature that defined the target could be distributed over a large or a small part of the entire stimulus. Only targets covering a larger area of the entire stimulus evoked stronger gamma-band activity than standards although the over-all stimulus size was identical for all stimuli. This increase in evoked activity resulted from stronger oscillatory power and not exclusively from stronger phase-locking. In contrast, N1 and P3 amplitudes were larger for target stimuli irrespective of the distribution of the relevant stimulus feature. These results are consistent with the notion that early gamma-band activity is generated by feature-selective neural assemblies the activity of which can in fact be modulated by top-down processes. This interaction, however, may be only detectable in scalp-recorded EEG if it affects a sufficient number of neural assemblies.

Aging Reduces Center-Surround Antagonism in Visual Motion Processing

Discriminating the direction of motion of a low-contrast pattern becomes easier with increasing stimulus area. However, increasing the size of a high-contrast pattern makes it more difficult for observers to discriminate motion. This surprising result, termed spatial suppression, is thought to be mediated by a form of center-surround suppression found throughout the visual pathway. Here, we examine the counterintuitive hypothesis that aging alters such center-surround interactions in ways that improve performance in some tasks. We found that older observers required briefer stimulus durations than did younger observers to extract information about stimulus direction in conditions using large, high-contrast patterns. We suggest that this age-related improvement in motion discrimination may be linked to reduced GABAergic functioning in the senescent brain, which reduces center-surround suppression in motion-selective neurons.

Spatial properties of photophobia.

To determine the spatial properties of stimuli that elicit photophobia (PP) in normal subjects: Does PP exhibit spatial summation? Are different parafoveal quadrants (superior, inferior, temporal, and nasal) of the retina differentially sensitive in PP? What is the relationship between PP sensitivity and retinal eccentricity? What is the relationship between the spatial properties of PP and the spatial distribution of macular pigment (MP)? A Maxwellian-view optical system with a xenon light source was used to present the stimuli. Four normal subjects viewed stimuli of various sizes, retinal locations, and one of two chromatic contents: xenon-white and a broadband orange. The intensity of the test stimulus was increased between trials until the PP threshold was reached. The squinting response corresponding to PP was assessed by electromyography and used as an objective criterion of PP. Three parameters were examined: stimulus size, parafoveal retinal locus (superior, inferior, temporal, and nasal), and retinal eccentricity (extending into the perifovea). Spatial profiles of MP were measured psychophysically using heterochromatic flicker photometry (HFP). Spatial summation for PP was found essentially to adhere to Piper's law (radiance proportional to square root of stimulus area). The PP response was greater to centrally than peripherally viewed targets. In this regard, MP acted as a spatially integrated filter in the attenuation of PP. The degree of spatial summation found for PP indicates that an increase of 1.0 log unit in field area results in an approximately 0.57-log-unit decrease in the radiance required to elicit PP. PP appears to serve the function of retinal photoprotection.

Spatial summation of heat pain within and across dermatomes in fibromyalgia patients and pain-free subjects

The mechanisms of spatial summation of pain (SSP) include pain coding dependent on impulse frequency and the number of recruited central neurons. However, SSP may also be influenced by pain inhibitory mechanisms, such as diffuse noxious inhibitory controls. Abnormal interactions between pain inhibitory mechanisms and SSP may be relevant for chronic pain conditions such as fibromyalgia (FM) and may help explain why widespread pain is characteristic for this chronic pain syndrome. The present study was designed to determine the difference of thermal SSP in the upper extremities between FM and normal control (NC) subjects, particularly within and across dermatomes of the hand. Fourteen NC and 19 FM subjects were enrolled in this study. SSP testing sessions involved immersion of each individual fingertip as well as stepwise immersion of the fingers, hands, and forearms in a hot water bath (46 °C) for 5s and 20s. In addition, immersion of several fingertips across dermatome C 7–C 8 was compared to progressive immersion of the index finger (dermatome C 7). These experiments demonstrated significant spatial summation of heat-induced pain in both FM and NC subjects. SSP was most extensive within the fingers, and became negligible as the stimulus area increased above the hand. Furthermore, SSP was more pronounced within one dermatome such as that of the index finger than across several dermatomes of the hand. These results were similar for both FM and NC subjects. Thus, mechanisms of SSP, including possible inhibitory factors that limit this relevant pain mechanism, appear to be similar for both FM and NC subjects.

Spatial integration of cold pressor pain sensation in humans

Spatial integration of cold pressor pain (CPP) in the hand was studied in healthy human subjects by measuring the latency to the ice water-induced first pain sensation with and without conditioning CPP. CPP alone showed a marked spatial summation effect. When conditioning and test CPP were applied at the same time, conditioning CPP suppressed test CPP both in an adjacent and a distant site. When test CPP was applied after the conditioning CPP (i.e. pain induced by conditioning CPP was considerably stronger than that evoked by test CPP) conditioning CPP suppressed the test CPP only in a distant site but enhanced it in an adjacent site. A decrease in the test stimulus area increased the suppressive effect by conditioning CPP. Thus, CPP shows spatial summation or inhibition depending on experimental parameters.

Spatial summation of pressure pain: effect of body region

The characteristics of spatial summation of pressure pain are not clear. Pressure pain threshold (PPT) and perceived pressure pain intensity were measured in the hand, painfree back and myofascial trigger points (MTPs) in the back, using three different stimulus areas (0.5, 1 and 2 cm 2). PPT decreased and perceived pain increased significantly with an increase in stimulation area in all the regions (e.g. PPT in the back, from 406±168 to 205±102 kPa, P<0.0001). The magnitude of spatial summation of pressure pain was not significantly different between the regions. However, PPT in the back was significantly higher compared to the hand and MTPs (e.g. for 2 cm 2: mean of 205±102 vs 175±75 and 159±72 kPa, P<0.01, respectively). Irrespective of body region, the quality of pain evoked with the large areas (1 and 2 cm 2) was of pressure whereas in the small area (0.5 cm 2) it was perceived as a prick. In conclusion, both PPT and perceived pressure pain intensity are subject to a considerable spatial summation in all the regions tested. The quality of pressure-evoked pain is probably determined by this spatial summation. Body region significantly affects the PPT level for a fixed stimulation area but not the magnitude of its spatial summation for areas up to 2 cm 2, which are probably within the receptive field of single spinal nociceptive neurons.

Effects of contrast and size on orientation discrimination

Motivated by the recent physiological finding that a neuron’s receptive field can increase in size by a factor of 2–4-fold at low contrast [Nat. Neurosci. 2 (1999) 733, Proc. Natl. Acad. Sci. USA 96 (1999) 12073], we sought to examine whether a psychophysical task might reflect the contrast dependent changes in the size/structure of a receptive field. We postulate that since spatial summation is not contrast invariant, a task that relies on the spatial structure of a receptive field, such as orientation discrimination, should also be affected by changes in contrast. Previously, orientation discrimination thresholds have been reported to be roughly independent of the contrast of a stimulus for most of the visible range of contrasts [i.e. J. Neurophysiol. 57 (1987) 773, J. Opt. Soc. Am. 6 (1989) 713, Vis. Res. 30 (1990) 449, Vis. Res. 39 (1999) 1631]. Here, we found large improvements in orientation discrimination with contrast that were dependent on stimulus area. Furthermore, the apparent constancy of orientation discrimination for large area stimuli is possibly a result of a floor effect on the threshold. Therefore we conclude that there is not strong evidence for contrast invariant orientation discrimination. We interpret these results in the context of recent neurophysiological results about the expansion of cortical cells’ receptive fields at low contrast.

Spatial integration in Glass patterns.

The extraction of a global orientation structure presumably has a different neural mechanism from that of the analysis of its local features. We investigated spatial integration within these two mechanisms using stimulus patterns composed of dot pairs (dipoles). The stimuli targeted local feature detection, contained no global configuration, but rather contained randomly oriented dipoles of a fixed length (the distance between the dots in a pair). For the detection of a global orientation structure, local dipole orientations were arranged in a concentric Glass pattern. Thresholds as a function of a stimulus area were determined by measuring the minimum proportion of dipoles among random-dot noise (signal-to-noise ratio) required for the detection of dipoles (features), as well as for the detection of an orientation structure. Thresholds for feature detection were significantly higher than those for the detection of the global structure--regardless of the stimulus size. Spatial integration, however, did not differ between the two tasks: the exponents of the power functions fitted to data for six observers were -0.48 +/- 0.07 for random dipole orientations and -0.62 +/- 0.1 for Glass patterns.

Effects of stimulus area on perceived speed of self-motion from optic flow

Effects of stimulus area on perceived speed of self-motion from optic flow

Orientation discrimination in visual noise using global and local stimuli

We have investigated orientation discrimination in visual noise using two types of high contrast, broadband stimuli. Discrimination thresholds are better for Local stimuli, in which the orientation signal is spatially limited, than for Global stimuli, in which the orientation signal extends across the entire stimulus. Performance improves with increasing stimulus area, reaching an optimum threshold of about 11% orientation signal. Thresholds were not influenced by brief presentation times or practice. These results, along with results from a simple computational model, suggest that human orientation discrimination for this kind of pattern is mediated by pooling local responses of low-level neural mechanisms and is limited by two stages of intrinsic neural noise.

Motion coherence thresholds in infants––different tasks identify at least two distinct motion systems

Optokinetic nystagmus (OKN) can be demonstrated from birth, but behavioural discrimination tasks such as habituation and preferential looking do not reveal any sensitivity to motion direction until a few weeks of age. This study compared coherence threshold for motion direction for OKN and preferential looking responses using closely comparable stimuli, in infants between 6 and 27 weeks of age. Infants were tested with two random dot motion displays, a uniform area of moving dots for OKN responses and a display in which a region was segmented on one side by differential motion direction for preferential looking responses. Coherence thresholds for each response were determined by a staircase method. For OKN responses, mean coherence thresholds were between 20% and 25%, with no significant improvement in OKN performance throughout the age range. Preferential looking thresholds were significantly higher than OKN thresholds. Preferential looking thresholds improved significantly with age, but remained higher than OKN thresholds throughout the age range tested. Experiments varying direction reversal frequency and stimulus area indicated that these differences were not simply a consequence of the spatial and temporal non-uniformity of the preferential looking stimulus. The differences in sensitivity levels and age trends for OKN and preferential looking responses we have found suggest that different directional mechanisms are involved in the two responses. We discuss the possibility that, in early infancy, OKN and preferential looking reflect the performance of subcortical and cortical directional mechanisms respectively.