Brain Hemodynamic Responses Research Articles

Identification of the regional variability of the brain hemodynamic response to spontaneous and step-induced CO2 changes using function expansions

The cerebrovascular bed is very sensitive to CO2 changes, particularly in respiratory-related areas, such as the brainstem. Therefore, the hemodynamic response to such changes is of interest as it quantifies this sensitivity. Here, we examine in detail the regional characteristics of the hemodynamic response to spontaneous and larger, externally induced step CO2 changes CO2 (end-tidal forcing) by utilizing BOLD functional magnetic resonance imaging (fMRI) measurements from healthy humans. We first obtain estimates of the impulse response between CO2 and BOLD signal in several anatomically and functionally defined regions of interest, using function expansions with different basis sets. These include the Laguerre basis, which has been widely used in linear and nonlinear systems identification particularly for biological/physiological systems, as well as different variants of gamma functions, which have been widely used in functional neuroimaging due to physiological considerations with regards to the characteristics of the BOLD response to external (sensory or other) stimuli. Based on the aforementioned comparisons, we perform the same analysis in smaller anatomical areas, considering voxel neighborhoods that span the entire image, in order to map key features of the hemodynamic response function such as peak value, time-to-peak and area, in finer spatial resolution.

Activation of the ventral striatum during aversive contextual conditioning in humans

The goal of this study was to investigate the function of the ventral striatum and brain regions involved in anxiety and learning during aversive contextual conditioning. Functional magnetic resonance imaging was used to assess the hemodynamic brain response of 118 healthy volunteers during a differential fear conditioning paradigm. Concurrently obtained skin conductance responses and self-reports indicated successful context conditioning. Increased hemodynamic responses in the ventral striatum during presentation of the conditioned visual stimulus that predicted the aversive event (CS+) compared to a second stimulus never paired with the aversive event (CS−) were observed in the late acquisition phase. Additionally, we found significant brain responses in the amygdala, hippocampus, insula and medial prefrontal cortex. Our data suggest the involvement of the ventral striatum during contextual fear conditioning, and underline its role in the processing of salient stimuli in general, not only during reward processing.

Depth-dependent cerebral hemodynamic responses following Direct Cortical Electrical Stimulation (DCES) revealed by in vivo dual-optical imaging techniques

We studied depth-dependent cerebral hemodynamic responses of rat brain following direct cortical electrical stimulation (DCES) in vivo with optical recording of intrinsic signal (ORIS) and near-infrared spectroscopy (NIRS). ORIS is used to visualize the immediate hemodynamic changes in cortical areas following the stimulation, whereas NIRS measures the hemodynamic changes originating from subcortical areas. We found strong hemodynamic changes in relation to DCES both in ORIS and NIRS data. In particular, the signals originating from cortical areas exhibited a tri-phasic response, whereas those originating from subcortical regions exhibited multi-phasic responses. In addition, NIRS signals from two different sets of source-detector separation were compared and analyzed to investigate the causality of perfusion, which demonstrated downstream propagation, indicating that the upper brain region reacted faster than the deep region.

Effects of sedative and non‐sedative antihistamine drugs on prefrontal cortex activities: towards pharmacological near‐infrared spectroscopy studies

SummaryHistamine H1‐receptor antagonists (antihistamines) are widely used for the treatment of allergic disorders in young children. It is well known that the newer antihistamine drugs elicit better performances of working memory and selective attention than the first‐generation drugs in this class. However, the neural correlates of the poorer performances associated with the first‐generation antihistamines remain relatively unknown. In this article, we review recent studies in our laboratory that examined the effects of antihistamine drugs on prefrontal cortex activities in adults and young children using near‐infrared spectroscopy (NIRS), an emerging brain imaging method that is suitable for psychological experiments. In the first study, we examined the prefrontal cortex activities while adult subjects performed a working memory task at 3 hours after taking a first‐generation antihistamine (ketotifen), a second‐generation antihistamine (epinastine), or a placebo. We found that cortical activation at the lateral prefrontal region increased during the performance of the working memory task in subjects administered epinastine or the placebo but not in those administered ketotifen. In the second study conducted in 15 healthy pre‐school children (mean age: 5.5 years), ketotifen significantly impaired the behavioural performance and cortical activation at the lateral prefrontal cortex in a working memory task compared with epinastine and the placebo. In the third study conducted in school‐aged children (mean age: 7.7 years), ketotifen significantly impaired the behavioural performance and cortical activation at the lateral prefrontal cortex compared with the placebo. There were no sedative effects on the neural responses or behavioural performance after epinastine administration. These studies demonstrate for the first time the differential sedation effects of first‐ and second‐generation antihistamines on brain haemodynamic responses in young children. We also discuss the utility of the NIRS technique in psychopharmacological studies of children.

Classification of frontal cortex haemodynamic responses during cognitive tasks using wavelet transforms and machine learning algorithms

Recent advances in neuroimaging demonstrate the potential of functional near-infrared spectroscopy (fNIRS) for use in brain–computer interfaces (BCIs). fNIRS uses light in the near-infrared range to measure brain surface haemoglobin concentrations and thus determine human neural activity. Our primary goal in this study is to analyse brain haemodynamic responses for application in a BCI. Specifically, we develop an efficient signal processing algorithm to extract important mental-task-relevant neural features and obtain the best possible classification performance. We recorded brain haemodynamic responses due to frontal cortex brain activity from nine subjects using a 19-channel fNIRS system. Our algorithm is based on continuous wavelet transforms (CWTs) for multi-scale decomposition and a soft thresholding algorithm for de-noising. We adopted three machine learning algorithms and compared their performance. Good performance can be achieved by using the de-noised wavelet coefficients as input features for the classifier. Moreover, the classifier performance varied depending on the type of mother wavelet used for wavelet decomposition. Our quantitative results showed that CWTs can be used efficiently to extract important brain haemodynamic features at multiple frequencies if an appropriate mother wavelet function is chosen. The best classification results were obtained by a specific combination of input feature type and classifier.

Neuronal inhibition and excitation, and the dichotomic control of brain hemodynamic and oxygen responses

Brain's electrical activity correlates strongly to changes in cerebral blood flow (CBF) and the cerebral metabolic rate of oxygen (CMRO(2)). Subthreshold synaptic processes correlate better than the spike rates of principal neurons to CBF, CMRO(2) and positive BOLD signals. Stimulation-induced rises in CMRO(2) are controlled by the ATP turnover, which depends on the energy used to fuel the Na,K-ATPase to reestablish ionic gradients, while stimulation-induced CBF responses to a large extent are controlled by mechanisms that depend on Ca(2+) rises in neurons and astrocytes. This dichotomy of metabolic and vascular control explains the gap between the stimulation-induced rises in CMRO(2) and CBF, and in turn the BOLD signal. Activity-dependent rises in CBF and CMRO(2) vary within and between brain regions due to differences in ATP turnover and Ca(2+)-dependent mechanisms. Nerve cells produce and release vasodilators that evoke positive BOLD signals, while the mechanisms that control negative BOLD signals by activity-dependent vasoconstriction are less well understood. Activation of both excitatory and inhibitory neurons produces rises in CBF and positive BOLD signals, while negative BOLD signals under most conditions correlate to excitation of inhibitory interneurons, but there are important exceptions to that rule as described in this paper. Thus, variations in the balance between synaptic excitation and inhibition contribute dynamically to the control of metabolic and hemodynamic responses, and in turn the amplitude and polarity of the BOLD signal. Therefore, it is not possible based on a negative or positive BOLD signal alone to decide whether the underlying activity goes on in principal or inhibitory neurons.

Memory in the neonate brain.

BackgroundThe capacity to memorize speech sounds is crucial for language acquisition. Newborn human infants can discriminate phonetic contrasts and extract rhythm, prosodic information, and simple regularities from speech. Yet, there is scarce evidence that infants can recognize common words from the surrounding language before four months of age.Methodology/Principal FindingsWe studied one hundred and twelve 1-5 day-old infants, using functional near-infrared spectroscopy (fNIRS). We found that newborns tested with a novel bisyllabic word show greater hemodynamic brain response than newborns tested with a familiar bisyllabic word. We showed that newborns recognize the familiar word after two minutes of silence or after hearing music, but not after hearing a different word.Conclusions/SignificanceThe data show that retroactive interference is an important cause of forgetting in the early stages of language acquisition. Moreover, because neonates forget words in the presence of some –but not all– sounds, the results indicate that the interference phenomenon that causes forgetting is selective.

Assessment of Pedophilia Using Hemodynamic Brain Response to Sexual Stimuli

Accurately assessing sexual preference is important in the treatment of child sex offenders. Phallometry is the standard method to identify sexual preference; however, this measure has been criticized for its intrusiveness and limited reliability. To evaluate whether spatial response pattern to sexual stimuli as revealed by a change in the blood oxygen level-dependent signal facilitates the identification of pedophiles. During functional magnetic resonance imaging, pedophilic and nonpedophilic participants were briefly exposed to same- and opposite-sex images of nude children and adults. We calculated differences in blood oxygen level-dependent signals to child and adult sexual stimuli for each participant. The corresponding contrast images were entered into a group analysis to calculate whole-brain difference maps between groups. We calculated an expression value that corresponded to the group result for each participant. These expression values were submitted to 2 different classification algorithms: Fisher linear discriminant analysis and κ -nearest neighbor analysis. This classification procedure was cross-validated using the leave-one-out method. Section of Sexual Medicine, Medical School, Christian Albrechts University of Kiel, Kiel, Germany. We recruited 24 participants with pedophilia who were sexually attracted to either prepubescent girls (n=11) or prepubescent boys (n=13) and 32 healthy male controls who were sexually attracted to either adult women (n=18) or adult men (n=14). Sensitivity and specificity scores of the 2 classification algorithms. The highest classification accuracy was achieved by Fisher linear discriminant analysis, which showed a mean accuracy of 95% (100% specificity, 88% sensitivity). Functional brain response patterns to sexual stimuli contain sufficient information to identify pedophiles with high accuracy. The automatic classification of these patterns is a promising objective tool to clinically diagnose pedophilia.

Neural Network Classification of Brain Hemodynamic Responses from Four Mental Tasks

We investigate subjects’ brain hemodynamic activities during mental tasks using a nearinfrared spectroscopy. A wavelet and neural network-based methodology is presented for recognition of brain hemodynamic responses. The recognition is performed by a single layer neural network classifier according to a backpropagation algorithm with two error minimizing techniques. The performance of the classifier varied depending on the neural network model, but the performance was usually at least 90%. The classifier usually converged faster and attained a somewhat greater level of performance when an input was presented with only relevant features. The overall classification rate was higher than 94%. The study demonstrates the accurate classifiablity of human brain hemodynamic useful in various brain studies.

P02-334 - Hemodynamic brain response to visual sexual stimuli is different between homosexual and heterosexual men

Many studies showed the differences in subjective response to sexual stimuli between heterosexual and homosexual men. However, the underlying neurobiological factors of sexual orientation are largely unknown. We addressed the question what is the major attribution of the expected differences in brain activation, i.e. neural circuits or different cognitive process. Twenty-eight healthy male volunteers, 14 heterosexuals and 14 homosexuals, were scanned by functional Magnetic Resonance Imaging while subjects were viewing different types of stimuli, i.e. heterosexual couple stimuli (HCS), gay couple stimuli (GCS), lesbian couple stimuli (LCS) and neutral stimuli (NS). SPM02 was used for data analysis. Rating of sexual attractiveness was assessed. Subjective sexual arousal was induced by HCS and GCS in heterosexual and homosexual men, respectively. And sexual disgust was induced by GCS and LCS in heterosexual and homosexual men, respectively. As compared to viewing NS, viewing sexual stimuli induced significant different brain activations most of which had characteristic for cognitive process. These observations suggested that different cognitive pattern was major attribution of different subjective response to sexual stimuli between heterosexual and homosexual men.

Neuronal correlates of repetition priming of familiar and unfamiliar visual objects: evidence from fMRI and MEG

Event Abstract Back to Event Neuronal correlates of repetition priming of familiar and unfamiliar visual objects: evidence from fMRI and MEG Uwe Friese1*, Benjamin Rahm2, Jochen Kaiser2 and Thomas Gruber1 1 University of Osnabrück, Germany 2 Gutenberg University, Germany Visual object recognition has been studied with various neuroimaging approaches including methods based on hemodynamic brain responses and electrophysiological measures. A common finding is the attenuation of brain activity during the processing of repeated stimuli in distributed cortical regions – a phenomenon often called repetition suppression. Due to differences in measuring modalities, experimental tasks, and procedures it is, however, difficult to compare previously published results directly. We conducted identical experiments with MEG and fMRI, respectively. Participants were repeatedly confronted with images of familiar and unfamiliar objects. Familiarity and repetition modulated fMRI-BOLD activity most prominently in bilateral occipito-temporal regions including the fusiform cortices. These regions have been associated with the processing of conceptual object representations in numerous fMRI studies. In the MEG study, we focused on the analysis of induced gamma band activity (iGBA) since synchronized oscillations in the gamma band range play an important role for the integration of distributed object representations. Source localization of iGBA revealed effects of familiarity and repetition in occipital and parietal cortex areas, partially overlapping with occipital regions found in the fMRI study. Both, the suppression of the BOLD signal and of iGBA are interpreted as a “sharpening” within cortical object representations which results in more efficient stimulus processing (i.e. priming). Our results demonstrate that while some overlap occurred for fMRI-BOLD and MEG-iGBA, each of the two methods might be sensitive to differential aspects of visual object processing. Keywords: fMRI, Memory Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Neural Bases of Memory and Learning Citation: Friese U, Rahm B, Kaiser J and Gruber T (2011). Neuronal correlates of repetition priming of familiar and unfamiliar visual objects: evidence from fMRI and MEG. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00421 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Uwe Friese, University of Osnabrück, Osnabrück, Germany, ufriese@uos.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Uwe Friese Benjamin Rahm Jochen Kaiser Thomas Gruber Google Uwe Friese Benjamin Rahm Jochen Kaiser Thomas Gruber Google Scholar Uwe Friese Benjamin Rahm Jochen Kaiser Thomas Gruber PubMed Uwe Friese Benjamin Rahm Jochen Kaiser Thomas Gruber Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effects of mobile phone electromagnetic fields: Critical evaluation of behavioral and neurophysiological studies

For the last two decades, a large number of studies have investigated the effects of mobile phone radiation on the human brain and cognition using behavioral or neurophysiological measurements. This review evaluated previous findings with respect to study design and data analysis. Provocation studies found no evidence of subjective symptoms attributed to mobile phone radiation, suggesting psychological reasons for inducing such symptoms in hypersensitive people. Behavioral studies previously reported improved cognitive performance under exposure, but it was likely to have occurred by chance due to multiple comparisons. Recent behavioral studies and replication studies with more conservative statistics found no significant effects compared with original studies. Neurophysiological studies found no significant effects on cochlear and brainstem auditory processing, but only inconsistent results on spontaneous and evoked brain electrical activity. The inconsistent findings suggest possible false positives due to multiple comparisons and thus replication is needed. Other approaches such as brain hemodynamic response measurements are promising but the findings are few and not yet conclusive. Rigorous study design and data analysis considering multiple comparisons and effect size are required to reduce controversy in this important field of research.

Significant correlation between autonomic nervous activity and cerebral hemodynamics during thermotherapy on the neck

Although local thermotherapy reduces mental stress and neck stiffness, its physiological mechanisms are still not fully understood. We speculated that local thermotherapy exerts its effect, in addition to its direct peripheral effects, through the central nervous system that is involved in controlling stress responses. In the present study, we investigated the effects of a heat- and steam-generating (HSG) sheet on cerebral hemodynamics and autonomic nervous activity using near-infrared spectroscopy (NIRS) and the electrocardiograms (ECGs). Thirteen healthy young female subjects participated in this study. HSG or simple (control) sheets were repeatedly applied to the neck for 120 s with 180 s intervals of rest between applications. During the experiment, brain hemodynamic responses (changes in Oxy-Hb, Deoxy-Hb, and Total-Hb) and autonomic nervous activity based on heart rate variability (HRV) were monitored. Subjective perception of neck stiffness and fatigue was significantly improved after application of the HSG sheet. NIRS findings indicated that the application of HSG sheets decreased Oxy-Hb concentration in the anterior-dorsal region of the medial prefrontal cortex (adMPFC), while increasing parasympathetic nervous activity and decreasing sympathetic nervous activity. Furthermore, changes in Oxy-Hb in the adMPFC were significantly and negatively correlated with those in parasympathetic nervous activity during application of the HSG sheet. These findings suggest that application of the HSG sheet to the neck region induced mental relaxation and ameliorated neck stiffness by modifying activity of the adMPFC.

Antihistamine effects on prefrontal cortex activity during working memory process in preschool children: A near-infrared spectroscopy (NIRS) study

Histamine H 1 receptor antagonists (antihistamines) are widely used for the treatment of allergic disorders in young children. This study examined the effects of antihistamine on prefrontal cortex activity in preschool children using near-infrared spectroscopy (NIRS), an emerging brain-imaging method suitable for psychological experiments, especially in young children. We examined the changes of oxygenated hemoglobin concentration in the prefrontal cortex while children performed a spatial working memory task, 3 h after taking a first-generation antihistamine (ketotifen), second-generation antihistamine (epinastine), or placebo. Fifteen healthy preschool children (mean age, 5.5 years) participated. Ketotifen significantly impaired behavioral performance and cortical activation at the lateral prefrontal cortex in the working memory task, compared with epinastine and placebo. There were no sedative effects on neural response or behavioral performance after epinastine administration. This paper demonstrates for the first time differential sedation effects of first- and second-generation antihistamines on brain hemodynamic response in young children. Also discussed is the utility of the NIRS technique in neuropsychopharmacological studies of children.

Correlation of visual-evoked hemodynamic responses and potentials in human brain

The interaction of brain hemodynamics and neuronal activity has been intensively studied in recent years to yield better understanding of brain function. We investigated the relationship between visual-evoked hemodynamic responses (HDRs), measured with near-infrared spectroscopy (NIRS), and neuronal activity in humans, approximated with the stimulus train duration or with visual-evoked potentials (VEPs). Concentration changes of oxyhemoglobin (HbO(2)) and deoxyhemoglobin (HbR) in tissue and VEPs were recorded simultaneously over the occipital lobe of ten healthy subjects to 3, 6, and 12 s pattern-reversing checkerboard stimulus trains having a reversal frequency of 2 Hz. We found that the area-under-the-curves (Sigma) of HbO(2) and HbR were linearly correlated with the stimulus train duration and with the SigmaVEP summed over the 3, 6, and 12 s stimulus train durations. The correlation was stronger between the SigmaHbO(2) or the SigmaHbR and the SigmaVEP than between the SigmaHbO(2) or the SigmaHbR and the stimulus train duration. The SigmaVEPs explained 55% of the SigmaHbO(2) and 74% of the SigmaHbR variance, whereas the stimulus train duration explained only 45% of the SigmaHbO(2) and 51% of the SigmaHbR variance. We used Sigma of the NIRS responses and VEPs because we wanted to incorporate all possible processes (e.g., attention, habituation, etc.) affecting the responses. The results indicate that the relationship between brain HDRs and VEPs is approximately linear for 3-12 s long stimulus trains consisting of checkerboard patterns reversing at 2 Hz. To interpret hemodynamic responses, the measurement of evoked potentials is beneficial compared to the use of indirect parameters such as the stimulus duration. In addition, interindividual differences in the HbO(2) and HbR responses may be partly explained with differences in the VEPs.

Inter-subject correlation of brain hemodynamic responses during watching a movie: localization in space and frequency

Cinema is a promising naturalistic stimulus that enables, for instance, elicitation of robust emotions during functional magnetic resonance imaging (fMRI). Inter-subject correlation (ISC) has been used as a model-free analysis method to map the highly complex hemodynamic responses that are evoked during watching a movie. Here, we extended the ISC analysis to frequency domain using wavelet analysis combined with non-parametric permutation methods for making voxel-wise statistical inferences about frequency-band specific ISC. We applied these novel analysis methods to a dataset collected in our previous study where 12 subjects watched an emotionally engaging movie “Crash” during fMRI scanning. Our results suggest that several regions within the frontal and temporal lobes show ISC predominantly at low frequency bands, whereas visual cortical areas exhibit ISC also at higher frequencies. It is possible that these findings relate to recent observations of a cortical hierarchy of temporal receptive windows, or that the types of events processed in temporal and prefrontal cortical areas (e.g., social interactions) occur over longer time periods than the stimulus features processed in the visual areas. Software tools to perform frequency-specific ISC analysis, together with a visualization application, are available as open source Matlab code.

Effects of sedative and nonsedative antihistamines on prefrontal activity during verbal fluency task in young children: a near-infrared spectroscopy (NIRS) study

Antagonists of histamine H(1) receptors (antihistamines) are widely used for the treatment of allergic disorders in children. These drugs' sedative effect on brain function, however, has been mostly examined in adults. The objective of this study was to examine the effects of anitihistamines on prefrontal cortex activity in young children using near-infrared spectroscopy (NIRS), a novel brain-imaging method. In 15 healthy children (mean age, 7.7 years), we examined changes of oxygenated hemoglobin concentration in the prefrontal cortex while they performed a verbal fluency task 3 h after taking a sedating antihistamine (ketotifen), nonsedating antihistamine (epinastine), or placebo. Ketotifen significantly impaired behavioral performance and cortical activation at the lateral prefrontal cortex compared with placebo. There were no sedative effects on neural response or behavioral performance after epinastine administration. NIRS revealed that sedating and nonsedating antihistamines exert differential effects on brain hemodynamic response in young children.

Double dissociation between action-driven and perception-driven conflict resolution invoking anterior versus posterior brain systems

The ability to select and integrate relevant information in the presence of competing irrelevant information can be enhanced by advance information to direct attention and guide response selection. Attentional preparation can reduce perceptual and response conflict, yet little is known about the neural source of conflict resolution, whether it is resolved by modulating neural responses for perceptual selection to emphasize task-relevant information or for action selection to inhibit pre-potent responses to interfering information. We manipulated perceptual information that either matched or did not match the relevant color feature of an upcoming Stroop stimulus and recorded hemodynamic brain responses to these events. Longer reaction times to incongruent than congruent color–word Stroop stimuli indicated conflict; however, conflict was even greater when a color cue correctly predicted the Stroop target's color (match) than when it did not (nonmatch). A predominantly anterior network was activated for Stroop-match and a predominantly posterior network was activated for Stroop-nonmatch. Thus, when a stimulus feature did not match the expected feature, a perceptually-driven posterior attention system was engaged, whereas when interfering, automatically-processed semantic information required inhibition of pre-potent responses, an action-driven anterior control system was engaged. These findings show a double dissociation of anterior and posterior cortical systems engaging in different types of control for perceptually-driven and action-driven conflict resolution.

Gestures Orchestrate Brain Networks for Language Understanding

Although the linguistic structure of speech provides valuable communicative information, nonverbal behaviors can offer additional, often disambiguating cues. In particular, being able to see the face and hand movements of a speaker facilitates language comprehension [1]. But how does the brain derive meaningful information from these movements? Mouth movements provide information about phonological aspects of speech [2-3]. In contrast, cospeech gestures display semantic information relevant to the intended message [4-6]. We show that when language comprehension is accompanied by observable face movements, there is strong functional connectivity between areas of cortex involved in motor planning and production and posterior areas thought to mediate phonological aspects of speech perception. In contrast, language comprehension accompanied by cospeech gestures is associated with tuning of and strong functional connectivity between motor planning and production areas and anterior areas thought to mediate semantic aspects of language comprehension. These areas are not tuned to hand and arm movements that are not meaningful. Results suggest that when gestures accompany speech, the motor system works with language comprehension areas to determine the meaning of those gestures. Results also suggest that the cortical networks underlying language comprehension, rather than being fixed, are dynamically organized by the type of contextual information available to listeners during face-to-face communication.

Hemodynamic Responses of Rat Brain Measured by Near-infrared Spectroscopy During Various Whisker Stimulations

NIRS (Near-infrared spectroscopy) is a relatively, new, non-invasive, and non-ionizing method of measuring hemodynamic responses in thick biological tissues such as the cerebral cortex. In this study, we measured the hemodynamic responses of the rat barrel cortex to whisker stimulation by using a frequency-domain NIRS system. We designed multiple optical probes comprising multi-mode optical fibers and manipulating arms, both of which can be easily applied to small animals. Various electrical stimulations were applied to rat whiskers at different voltage levels and stimulation frequencies. Our results show that the hemodynamic responses are highly dependent on the stimulation voltage level, and not so much on stimulation frequency. This paper suggests that NIRS technology is highly suitable for the study of small animal brains.