Hemodynamic responses to visual stimulation in occipital and frontal cortex of newborn infants: a near-infrared optical topography study

A near-infrared optical topography (OT) was used to reveal spatio-temporal changes in the cerebral oxygenation of newborn infants in response to brief visual stimulation. Newborn infants were presented 3 s stroboscopic light flashing at 14 Hz during spontaneous sleep. Event-related changes in oxy- and deoxyhemoglobin ([oxy-Hb] and [deoxy-Hb]) were observed over the occipital and frontal cortex. The visual stimulus produced statistically significant increases in oxyhemoglobin not only in the occipital cortex but also in the prefrontal cortex. These results suggest that the cerebrovascular coupling is already functioning in newborn’s brain. The prefrontal activation implies that it may contribute to early processing of sensory signals.     

Changes in hemoglobin concentration in the lateral occipital regions during shape recognition: a near-infrared spectroscopy study

By using near-infrared spectroscopy (NIRS), we measured the changes in the oxygenated and deoxygenated hemoglobin (oxy-Hb and deoxy-Hb, respectively) concentrations while performing visual tasks. We conducted experiments using two tasks: a shape recognition task and a position recognition task. It was found that the oxy-Hb concentration was substantially higher in the lateral occipital regions during shape recognition than during position recognition. The changes in the oxy-Hb concentration were considered to reflect the activation difference between the two tasks. No difference was observed in the oxy-Hb concentration during the memorization of shape and memorization of position. The deoxy-Hb concentration was different between the two tasks only when different stimuli were used but not when identical stimuli were used. In addition, it was suggested that the deoxy-Hb concentration is more sensitive to activation difference between the hemispheres and the activation at some regions. Measurements of the oxy-Hb and deoxy-Hb concentrations would reflect different aspects of cortical activations. The present results showed that measuring the oxy-Hb and deoxy-Hb concentrations separately can differentiate the activation of the regional cortical functions.     

Temporal analysis of the flow from V1 to the extrastriate cortex in humans

We previously examined the cortical processing in response to somatosensory, auditory and noxious stimuli, using magnetoencephalography in humans. Here, we performed a similar analysis of the processing in the human visual cortex for comparative purposes. After flash stimuli applied to the right eye, activations were found in eight cortical areas: the left medial occipital area around the calcarine fissure (primary visual cortex, V1), the left dorsomedial area around the parietooccipital sulcus (DM), the ventral (MOv) and dorsal (MOd) parts of the middle occipital area of bilateral hemispheres, the left temporo-occipito-parietal cortex corresponding to human MT/V5 (hMT), and the ventral surface of the medial occipital area (VO) of the bilateral hemispheres. The mean onset latencies of each cortical activity were (in ms): 27.5 (V1), 31.8 (DM), 32.8 (left MOv), 32.2 (right MOv), 33.4 (left MOd), 32.3 (right MOv), 37.8 (hMT), 46.9 (left VO), and 46.4 (right VO). Therefore the cortico-cortical connection time of visual processing at the early stage was 4-6 ms, which is very similar to the time delay between sequential activations in somatosensory and auditory processing. In addition, the activities in V1, MOd, DM, and hMT showed a similar biphasic waveform with a reversal of polarity after 10 ms, which is a common activation profile of the cortical activity for somatosensory, auditory, and pain-evoked responses. These results suggest similar mechanisms of the serial cortico-cortical processing of sensory information among all sensory areas of the cortex.     

Seeing faces activates three separate areas outside the occipital visual cortex in man

We have examined magnetic cortical responses of 15 healthy humans to 46 different pictures of faces. At least three areas outside the occipital visual cortex appeared to be involved in processing this input, 105-560 ms after the stimulus onset. The first active area was near the occipitotemporal junction, the second in the inferior parietal lobe, and the third in the middle temporal lobe. The source in the inferior parietal lobe was also activated by other simple and complex visual stimuli.     

Movement-related cortical activation with voluntary pinch task: simultaneous monitoring of near-infrared spectroscopy signals and movement-related cortical potentials

This study was designed to evaluate hemodynamic and electrophysiological motor cortex responses to voluntary finger pinching in humans, with simultaneous recording of near-infrared spectroscopy (NIRS) signals and movement-related cortical potentials (MRCP). Six healthy, right-handed subjects performed 100 trials of voluntary right-thumb index-finger pinching with about a 10-second interval at their own pace. Throughout the session, 48 regions over the bilateral motor cortex were assessed by NIRS, while MRCP and electromyogram (EMG) were simultaneously monitored. MRCP started 1536±58 ms before EMG onset and peaked 127±24 ms after EMG onset. NIRS data showed bilateral prefrontal cortex at 0.5±0.1 s before EMG onset and bilateral dorsal premotor cortex activations at 0.6±0.1 s before EMG onset. The hand area of the sensorimotor cortex was activated left-dominantly, seen obviously peaked at 3.7±0.2 s after EMG onset. The comparison between MRCP and NIRS results raised the possibility that the vascular response to neural activity occurs within 4 s with a voluntary pinch task. These results indicate that our technique allows detailed study of the motor control. Our method is a promising strategy for event-related motor control and neurovascular coupling studies.     

A functional magnetic resonance imaging study of local/global processing with stimulus presentation in the peripheral visual hemifields

When stimuli are presented in the left or right visual fields, hemispheric specialization for global and local processing in occipital areas is attenuated. Using functional magnetic resonance imaging, we investigated how this attenuation is compensated for when information must cross the corpus callosum to reach the areas specialized for global and local processing. We presented hierarchically nested letters (e.g. a large E made of smaller E's) to the right or the left visual hemifield while subjects fixated centrally. In half the trials, subjects indicated whether the global aspect and in the other half whether the local aspect of the stimulus matched a pre-specified target letter. Visual hemifield presentations showed the expected contralateral activations of occipital cortex. The main effects of locally or globally directed attention did not show any differential occipital activations, but the right anterior cingulate cortex was activated differentially during local processing. Region-of-interest-based analyses showed increased neural activity in left posterior occipital cortex during local processing when stimuli were presented in the left hemifield. During global processing with stimulus presentation to the right hemifield, the right posterior occipital cortex was activated. Activation of right anterior cingulate cortex during local processing is likely to reflect the suppression of global processing precedence in order to select correctly the local stimulus level. The activations in left (local) and right (global) occipital areas are likely to reflect the top-down augmentation of stimulus information that has been degraded by callosal crossing in order to access the hemisphere specialized for local or global processing.     

Distinct time scales in cortical discrimination of natural sounds in songbirds

Understanding how single cortical neurons discriminate between sensory stimuli is fundamental to providing a link between cortical neural responses and perception. The discrimination of sensory stimuli by cortical neurons has been intensively investigated in the visual and somatosensory systems. However, relatively little is known about discrimination of sounds by auditory cortical neurons. Auditory cortex plays a particularly important role in the discrimination of complex sounds, e.g., vocal communication sounds. The rich dynamic structure of such complex sounds on multiple time scales motivates two questions regarding cortical discrimination. How does discrimination depend on the temporal resolution of the cortical response? How does discrimination accuracy evolve over time? Here we investigate these questions in field L, the analogue of primary auditory cortex in zebra finches, analyzing temporal resolution and temporal integration in the discrimination of conspecific songs (songs of the bird's own species) for both anesthetized and awake subjects. We demonstrate the existence of distinct time scales for temporal resolution and temporal integration and explain how they arise from cortical neural responses to complex dynamic sounds.     

Single-trial classification of antagonistic oxyhemoglobin responses during mental arithmetic

Near-infrared spectroscopy (NIRS) is a non-invasive optical technique that can be used for brain–computer interfaces (BCIs) systems. A common challenge for BCIs is a stable and reliable classification of single-trial data, especially for cognitive (mental) tasks. With antagonistic activation pattern, recently found for mental arithmetic (MA) tasks, an improved online classification for optical BCIs using MA should become possible. For this investigation, we used the data of a previous study where we found antagonistic activation patterns (focal bilateral increase of [oxy-Hb] in the dorsolateral prefrontal cortex in parallel with a [oxy-Hb] decrease in the medial area of the anterior prefrontal cortex) in eight subjects. We used the [oxy-Hb] responses to search for the best antagonistic feature combination and compared it to individual features from the same regions. In addition, we investigated the use of antagonistic [deoxy-Hb], total hemoglobin [Hbtot] and pairs of [oxy-Hb] and [deoxy-Hb] features as well as the existence of a group-related feature set. Our results indicate that the use of the antagonistic [oxy-Hb] features significantly increases the classification accuracy from 63.3 to 79.7%. These results support the hypothesis that antagonistic hemodynamic response patterns are a suitable control strategy for optical BCI, and that only two prefrontal NIRS channels are needed for good performance.     

Cognitive control mechanisms resolve conflict through cortical amplification of task-relevant information

A prominent model of how the brain regulates attention proposes that the anterior cingulate cortex monitors the occurrence of conflict between incompatible response tendencies and signals this information to a cognitive control system in dorsolateral prefrontal cortex. Cognitive control is thought to resolve conflict through the attentional biasing of perceptual processing, emphasizing task-relevant stimulus information. It is not known, however, whether conflict resolution is mediated by amplifying neural representations of task-relevant information, inhibiting representations of task-irrelevant information, or both. Here we manipulated trial-by-trial levels of conflict and control during a Stroop task using face stimuli, while recording hemodynamic responses from human visual cortex specialized for face processing. We show that, in response to high conflict, cognitive control mechanisms enhance performance by transiently amplifying cortical responses to task-relevant information rather than by inhibiting responses to task-irrelevant information. These results implicate attentional target-feature amplification as the primary mechanism for conflict resolution through cognitive control.     

Activation of the visual cortex imaged by 24-channel near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a noninvasive technique for continuous monitoring of the amounts of total hemoglobin (total-Hb), oxygenated hemoglobin, (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb). The purpose of the present study was to demonstrate the utility of NIRS in functional imaging of the human visual cortex. A new NIRS imaging system enabled measurements from 24 scalp locations covering a 9 cm sq area. Topographic images were obtained from interpolations of the concentration changes between measurement points. Five healthy subjects between 25 and 49 years of age were investigated. After a resting baseline period of 50 s, the subjects were exposed to a visual stimulus for 20 s, followed by a 50 s resting period in a dimly lit, sound attenuating room. The visual stimulus was a circular, black and white, alternating checkerboard. In four of five subjects the visual cortex was the most activated area during visual stimulation. This is the first reported use of a NIRS-imaging system for assessing hemodynamic changes in the human visual cortex. The typical hemodynamic changes expected were observed; the total-Hb and oxy-Hb increased just after the start of stimulation and plateaued after 10 s of the stimulation period.     

Long-term voltage-sensitive dye imaging reveals cortical dynamics in behaving monkeys

A novel method of chronic optical imaging based on new voltage-sensitive dyes (VSDs) was developed to facilitate the explorations of the spatial and temporal patterns underlying higher cognitive functions in the neocortex of behaving monkeys. Using this system, we were able to explore cortical dynamics, with high spatial and temporal resolution, over period of 相似文献   

Subgenual cingulate and visual cortex responses to sad faces predict clinical outcome during antidepressant treatment for depression

BackgroundPrevious follow-up studies indicate that increased visual cortical, ventral cingulate and subcortical responses of depressed individuals to sad facial stimuli, but not happy stimuli could represent reversible markers of disease severity. We hypothesized that greater responses in these areas to sad stimuli, but not happy stimuli, would predict better subsequent clinical outcome. We also explored areas that would predict a poor outcome.MethodsTwelve melancholically depressed individuals in the early stages of antidepressant treatment in a secondary care setting participated in two experiments comparing responses to varying intensities of sad and happy facial stimuli, respectively, using event related functional MRI. They repeated the experiments after a mean delay of 12 weeks of treatment.ResultsThere was a variation in response to treatment. Greater right visual cortex and right subgenual cingulate (R-BA25) responses to sad stimuli, but not happy stimuli, in the early stages of treatment were associated with a good clinical outcome. Greater ventrolateral prefrontal cortex responses to either stimulus type were associated with a relatively poor outcome.LimitationsThe sample size was modest and patients were taking a variety of antidepressants.ConclusionsRight subgenual cingulate and right visual cortical responses to sad stimuli predict good clinical outcome in the context of antidepressant treatment for severe depression in a naturalistic setting. Ventrolateral prefrontal cortex activity may indicate poor prognosis due to its relationship with negative rumination.     

The temporal pattern of motion in depth perception derived from ERPs in humans

Former studies have demonstrated the cortical regions being involved in visual motion processing. The strength of neuronal activation was found to depend on the direction of motion. In particular the detection of optic flow towards the observer seems of particular importance due to its obvious biological relevance. We used event related potentials (ERPs) to add data of the temporal dynamics of this neuronal processing. Using current density reconstruction, source maxima of differential activation in motion in depth versus planar motion in the time range from 50 to 400 ms after stimulus onset were localized, and the time courses of activation were elaborated. Source reconstruction revealed six regions contributing significant source activity related to the perception of motion in depth: occipital pole, bilateral fusiform gyrus, right lateral superior occipital cortex and bilateral superior parietal cortex. Our data provide evidence for an early involvement of visual occipital cortex in the perception of motion in depth stimuli, followed by activation within parietal cortex, presumably associated with attention information processing. Sub-dividing the effects of the direction of the stimuli in motion in depth perception, optic flow directed towards the observer-induced stronger activation, but this differential activation excluded the parietal cortex. Thus the temporal deconvolution of the electrophysiological data suggests that the differential processing of approaching stimuli is initiated at an early stage of visual perception within the visual association area.     

Manifestation of scotomas created by transcranial magnetic stimulation of human visual cortex.

Reduced visual performance under transcranial magnetic stimulation (TMS) of human visual cortex demonstrates suppression whose spatial extent is not directly visible. We created an artificial scotoma (region missing from a visual pattern) to directly visualize the location, size and shape of the TMS-induced suppression by following a large-field, patterned, visual stimulus with a magnetic pulse. The scotoma shifted with coil position according to known topography of visual cortex. Visual suppression resulted in pattern-dependent distortion, and the scotoma was filled in with temporally adjacent stimuli, suggesting spatial and temporal completion mechanisms. Thus, perceptual measurements of TMS-induced suppression may provide information about cortical processing via neuronal connections and temporal interactions of neural signals.     

An artificial neural network model of orienting attention toward threatening somatosensory stimuli

An artificial neural network model was designed to test the threat detection hypothesis developed in our experimental studies, where threat detector activity in the somatosensory association areas is monitored by the medial prefrontal cortex, which signals the lateral prefrontal cortex to redirect attention to the threat. As in our experimental studies, simulated threat-evoked activations of all three brain areas were larger when the somatosensory target stimulus was unattended than attended, and the increase in behavioral reaction times when the target stimulus was unattended was smaller for threatening than nonthreatening stimuli. The model also generated a number of novel predictions, for example, the effect of threat on reaction time only occurs when the target stimulus is unattended, and the P3a indexes prefrontal cortex activity involved in redirecting attention toward response processes on that trial and sensory processes on subsequent trials.     

Attentional effects in the visual pathways: a whole-brain PET study

Attentional effects in the visual pathways were investigated by contrasting the distribution of regional cerebral blood flow (rCBF) measured by H₂ ¹⁵O positron emission tomography (PET) during performance of a shape-matching task with the distribution of rCBF during a less demanding color-matching task. The two tasks were performed using the same stimuli: pairs of colored random shapes shown at a fixed rate (2 s per pair). In the shape-matching task, the subjects determined whether the two stimuli were the same in shape regardless of differences in size or color. In the color-matching task, the subjects determined whether the two stimuli were the same in color regardless of differences in size or shape. Mean reaction time for shape-matching exceeded mean reaction time for color-matching by nearly 200 ms. The corresponding shape-color comparison showed extensive bilateral increases in rCBF in visual areas in the occipital and parietal lobes, including the primary visual cortex. Subcortical activations were found in cerebellum (particularly the vermis) and in the thalamus with the focus in a region comprising the lateral geniculate nucleus, the pulvinar, and adjacent parts of the reticular nucleus. Frontal activations were found in a region that seems implicated in visual short-term memory (posterior parts of the superior sulcus and the middle gyrus). The reverse, color-shape comparison showed bilateral increases in rCBF in the anterior cingulate gyri, superior frontal gyri, and superior and middle temporal gyri. The attentional effects found by the shape-color comparison in the thalamus and the primary visual cortex may have been generated by feedback signals preserving visual representations of selected stimuli in short-term memory. Electronic Publication     

Single-neuron responses to emotional visual stimuli recorded in human ventral prefrontal cortex

Both lesion and functional imaging studies in humans, as well as neurophysiological studies in nonhuman primates, demonstrate the importance of the prefrontal cortex in representing the emotional value of sensory stimuli. Here we investigated single-neuron responses to emotional stimuli in an awake person with normal intellect. Recording from neurons within healthy tissue in ventral sites of the right prefrontal cortex, we found short-latency (120-160 ms) responses selective for aversive visual stimuli.     

Stimulus selection via differential response latencies in visual cortical area V4

Any given region of the cerebral cortex gets multiple inputs, and how these inputs are combined or selected is a key component of cortical function. Experiments in brain slices or other reduced preparations have shown that excitatory inputs to cortex produce a delayed feed-forward inhibition, which suggests that the relative timing of inputs at the scale of tens of milliseconds is crucial to cortical operation. Other mechanisms, such as synaptic depression and feedback inhibition, have also been shown to produce strong effects on this timescale. Thus, the relative timing of inputs should be fundamental in determining how a given region of cortex selects or combines its inputs. A rhesus monkey (Macaca mulatta) was trained to fixate on a spot of light for juice reward. Isolated single units in visual cortical area V4 were recorded using standard microelectrode techniques. Two visual stimuli were positioned such that each alone elicited a strong response. The stimuli were presented both separately and in combination, and their contrast and relative onset timing were varied. In general, the response of each neuron to two stimuli was locked to the response to that single stimulus that produced the shortest latency. A partial exception was that the responses to low-contrast stimuli were often less effective at suppressing later-arriving responses to high-contrast stimuli. The presentation of two stimuli in the receptive field of a visual cortical neuron is proposed as a model system for how changes in the relative timing of inputs affect cortical function in the intact system.     

Responses to natural scenes in cat V1

Studies on processing in primary visual areas often use artificial stimuli such as bars or gratings. As a result, little is known about the properties of activity patterns for the natural stimuli processed by the visual system on a daily basis. Furthermore, in the cat, a well-studied model system for visual processing, most results are obtained from anesthetized subjects and little is known about neuronal activations in the alert animal. Addressing these issues, we measure local field potentials (lfp) and multiunit spikes in the primary visual cortex of awake cats. We compare changes in the lfp power spectra and multiunit firing rates for natural movies, movies with modified spatio-temporal correlations as well as gratings. The activity patterns elicited by drifting gratings are qualitatively and quantitatively different from those elicited by natural stimuli and this difference arises from both spatial as well as temporal properties of the stimuli. Furthermore, both local field potentials and multiunit firing rates are most sensitive to the second-order statistics of the stimuli and not to their higher-order properties. Finally, responses to natural movies show a large variability over time because of activity fluctuations induced by rapid stimulus motion. We show that these fluctuations are not dependent on the detailed spatial properties of the stimuli but depend on their temporal jitter. These fluctuations are important characteristics of visual activity under natural conditions and impose limitations on the readout of possible differences in mean activity levels.     

Differentiating cortical areas related to pain perception from stimulus identification: temporal analysis of fMRI activity.

In a recent functional magnetic resonance imaging study (fMRI), we reported the cortical areas activated in a thermal painful task and compared the extent of overlap between this cortical network and those activated during a vibrotactile task and a motor task. In the present study we examine the temporal properties of the cortical activations for all three tasks and use linear systems identification techniques to functionally differentiate the cortical regions identified in the painful thermal task. Cortical activity was examined in the contralateral middle third of the brain of 10 right-handed subjects, using echo-planar imaging and a surface coil. In another eight subjects the temporal properties of the thermal task were examined psychophysically. The fMRI impulse response function was estimated from the cortical activations in the vibrotactile and motor tasks and shown to correspond to earlier reports. Given the fMRI impulse response function and the time courses for the thermal stimulus and the associated pain ratings, predictor functions were generated. The correlation between these predictor functions and cortical activations in the painful thermal task indicated a gradual transition of information processing anteroposteriorly in the parietal cortex. Within this region, activity in the anterior areas more closely reflected thermal stimulus parameters, whereas activity more posteriorly was better related to the temporal properties of pain perception. Insular cortex at the level of the anterior commissure was the region best related to the thermal stimulus, and Brodmann's area 5/7 was the region best related to the pain perception. The functional implications of these observations are discussed.