Relation between regional functional MRI activation and vascular reactivity to carbon dioxide during normal aging

Recent blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging studies have shown a reduction of cerebral activation during aging, which may be associated with age-related changes of the cerebral vascular system. The authors used a global hypercapnic breath-holding challenge to define nonneuronal contributions to a significantly reduced activation in the primary sensorimotor cortex during finger tapping in a group of old (n = 6; mean age 65 years) compared with a group of young (n = 6; mean age 27 years) subjects. Within significantly activated voxels in both groups during finger tapping, the mean BOLD signal amplitudes were significantly smaller in the group of older subjects for both tasks. In those voxels showing significant activation only in young subjects during finger tapping, the response to hypercapnia was also greatly diminished in older subjects. The attenuated hypercapnic BOLD signal response in older subjects within this region suggests that age-dependent changes of the cerebral vasculature may alter the neuronal-vascular coupling. In older subjects, cerebral vessels may not react as effectively in response to a vasodilating stimulus, which will lead to differences in the number of voxels that pass a criterion threshold despite similar neuronal activation.

A comparative pilot-scale study of the performance of conventional activated sludge and membrane bioreactors under limiting operating conditions

The behavior of the conventional activated-sludge (CAS) process was compared to that of the membrane bioreactor (MBR) process under limiting operating conditions; that is, at a low solids retention time (SRT) and hydraulic residence time (HRT). The SRT was varied from 2 to 7 days, and the HRT ranged from 5 to 18 hours. The comparison was carried out in terms of nitrification and denitrification kinetics and in terms of the carbon and nitrogen removal performance of these processes. The study involved two pilot-scale units: a CAS unit with a 9-m3 aeration tank and a 225-L MBR. Both of these units were installed and run under real process conditions at a wastewater treatment plant in Evry, France. In the case of the MBR process, the specific nitrification rates, rN, and the specific denitrification rates, rDN, increased as SRT was reduced from 6.5 days to 2 days. This trend was reversed and the rN and rDN decreased only when the HRT was reduced to 5 hours. A similar behavior was observed in the case of the CAS process, although rN and rDN increased only when the SRT was reduced to as low as 4 days; below this value, the rates dropped considerably. It seems that the presence of the membrane renders the MBR more robust by preventing the washout of nitrifiers at low SRT and HRT. Besides the structure and size distribution of the MBR, flocs are more favorable to intraparticle mass transfer than those of the CAS process and could explain the higher nitrification kinetics observed with the MBR process. In all cases, the carbon and nitrogen removal performance of the MBR process was better than that of the CAS system.

Why are smiles contagious? An fMRI study of the interaction between perception of facial affect and facial movements

In human communication there is often a close relationship between the perception of an emotionally expressive face and the facial response of the viewer himself. Whereas perception and generation of facial expressions have been studied separately with functional imaging methods, no studies exist on their interaction. We combined the presentation of emotionally expressive faces with the instruction to react with facial movements predetermined and assigned. fMRI was used in an event related design to examine healthy subjects while they regarded happy, sad, or neutral faces and were instructed to simultaneously move the corners of their mouths either (a). upwards or (b). downwards, or (c). to refrain from movement. The subjects' facial movements were recorded with an MR-compatible video camera. Movement latencies were shortened in congruent situations (e.g. the presentation of a happy face and combined with upward movements) and delayed in non-congruent situations. Dissonant more than congruent stimuli activated the inferior prefrontal cortex and the somatomotor cortex bilaterally. The congruent condition, in particular when seeing a happy face, activated the medial basotemporal lobes (hippocampus, amygdala, parahippocampal region). We hypothesize that this region facilitates congruent facial movements when an emotionally expressive face is perceived and that it is part of a system for non-volitional emotional facial movements.

Reorganization in the primary motor cortex after spinal cord injury - A functional Magnetic Resonance (fMRI) study

Activation maps in the primary motor cortex (M1) were investigated in three patients with complete spinal cord injury (SCI) at level TH3, TH7 and TH9 and in one patient with an incomplete spinal cord injury at level L1 during right elbow (4 patients), right thumb (4 patients), bilateral lip (2 patients) and right foot (3 patients during imagined, 1 patient during executed) movements using functional Magnetic Resonance Imaging (fMRI). Compared to controls fMRI activation maps of patients with complete paraplegia showed a cranial displacement of the activation maxima in the contralateral primary motor cortex during elbow movement of 13.3mm, whereas the maxima of thumb and lip movements were not altered. The patient with an incomplete spinal cord injury revealed no displacement of elbow activation maxima. The reorganization is likely to occur on the cortical and not on the spinal level.

Differential expression of L- and S-MAG upon cAMP stimulated differentiation in oligodendroglial cells

Myelin-associated glycoprotein (MAG), an immunoglobulin-like cell signaling protein involved in axon-glial interactions, displays two intracellular C-termini as a result of alternative mRNA splicing. During brain development, the two MAG mRNAs that encode L-MAG and S-MAG differ in their relative abundance. We have investigated the differential expression of L- and S-MAG upon cAMP treatment in the oligodendroglial cell line Oli-neu, a cell line able to differentiate in vitro. We have engineered GFP and VSVG fusions by small insertions into the alternatively spliced exons of the cloned MAG gene and reintroduced them into Oli-neu cells. The individually tagged MAG isoforms were expressed under the control of the MAG promoter and regulatory region. In this system, L-MAG was the predominant isoform before the stimulation of cells with cAMP, whereas upon cAMP treatment the S-MAG isoform was predominantly expressed in cells with a high degree of morphological differentiation. We suggest that the regulation of the MAG alternative splicing and the morphological differentiation in oligodendrocytes are controlled both by the same cAMP-responsive differentiation step.

Comparison of representational maps using functional magnetic resonance imaging and transcranial magnetic stimulation

OBJECTIVE

Comparison of functional magnetic resonance imaging (fMRI) representational maps, that were generated during voluntary thumb abduction, hand dorsiflexion and foot elevation to amplitude maps of motor-evoked potentials (MEPs) elicited by single transcranial magnetic stimulation (TMS) administered to cortical motor representation areas of the muscles of the thenar eminence, extensor carpi radialis and tibialis anterior muscles.

METHODS

Stimulus locations that produced maximal motor-evoked potential amplitudes were compared to fMRI activation maxima in three-dimensional (3D)-space and in a 2D-projection using a novel technique that allowed fMRI activation sites to be projected onto the surface of the brain.

RESULTS AND CONCLUSIONS

When analyzing pooled data from all target muscles, the location of projected fMRI and TMS activation maxima on the cortical surface differed by an average 13.9 mm. The differences in 3D distances were particularly large for representation areas of lower leg muscles. 3D distances between fMRI activation maxima and highest MEP site in TMS correlated significantly with higher TMS thresholds. These observations strongly suggest that higher TMS excitation thresholds and lower MEP amplitudes are largely due to the absolute distance between the stimulation site and the excitable cortical tissue targeting this muscle. After the projection 4 out of 5 representation sites as evaluated by TMS were located anterior to the fMRI activation maxima, an observation which may due to the orientation of the magnetic field induced by the current in the coil. The representation sites as evaluated with both methods were specific for the type of movement: distances between representation maxima of the same movements were significantly smaller than those within different movements. Nevertheless, fMRI and TMS provide complementary information, which is discussed on the basis of the functional map observed with both methods.

Proton magnetic resonance spectroscopy with metabolite nulling reveals regional differences of macromolecules in normal human brain

PURPOSE

To quantify the macromolecular content in different anatomic brain regions and to evaluate an age dependency of the macromolecular concentrations.

MATERIAL AND METHODS

A short echo time Stimulated Echo Acquisition Mode (STEAM) sequence was used without and with inversion recovery metabolite nulling in 8-12 healthy volunteers. Quantitation was achieved by an extended LCModel, and macromolecular resonances at 0.9, 1.4, 2.1, and 3.0 ppm were evaluated.

RESULTS

In the cerebellum, the 1.4, 2.1, and 3.0 ppm resonances were highest compared to all other regions (P < 0.02); the 0.9 ppm resonance was significantly higher than that of pons (P < 0.01). In the motor cortex, the 0.9, 1.4, and 2.1 ppm resonances were higher than those of white matter and pons (P < 0.02). Pons and white matter did not differ significantly from each other. A significant correlation of the macromolecular concentrations with the age could not be found.

CONCLUSION

There were higher macromolecular concentrations in the cerebellum and motor cortex than in pons or white matter. These were probably due to the higher portions of gray matter in these volumes of interest (VOIs) than in the other regions.

Two types of ipsilateral reorganization in congenital hemiparesis: a TMS and fMRI study

Reorganization after early brain injuries is not only determined by the maturational stage of the CNS at the time of the insult (timing), but also by the structural properties, location and extent of the lesion. This study addresses the impact of different lesion extents on the type of reorganization induced in a cohort of patients with lesions of uniform structure and location (unilateral periventricular defects) and similar timing (early third trimester of pregnancy). Twelve young adult patients with congenital hemiparesis and 10 age-matched controls were studied. The severity of structural damage to hand motor projections of the cortico-spinal tract was assessed on semi-coronal MRI reconstructions along anatomical landmarks of cortico-spinal tract somatotopy. The functional integrity of these crossed cortico-spinal projections in the affected hemisphere, as well as the presence of any abnormal ipsilateral projections to the paretic hand, was examined by transcranial magnetic stimulation (TMS). Cortical activation during simple voluntary hand movements was studied by functional MRI (fMRI). Patients with small lesions (SL; n = 4) and only mild hand motor impairment possessed intact crossed cortico-spinal projections to the paretic hand, whereas no motor response could be elicited by TMS of the affected hemisphere in those with large lesions (LL; n = 6) and more severe hand motor impairment. Evidence for compensatory recruitment of the unaffected hemisphere was found in both subgroups. In the SL group, fMRI demonstrated ipsilateral activation of premotor areas, without any abnormal projections to the paretic hand originating from these sites. In the LL group, such abnormal ipsilateral projections to the paretic hand were indeed found, and fMRI confirmed cortical activation of an abnormal ipsilateral hand motor representation in the primary sensorimotor region of the unaffected hemisphere. Two patients with intermediate-sized lesions presented combined features of both groups (SL, LL). In conclusion, this study provides evidence that the type of cortico-spinal reorganization depends on the extent of the brain lesion. We propose that involvement of the ipsilateral hemisphere can be (i) of the premotor type, i.e. without ipsilateral motor projections but with significant activation of ipsilateral premotor areas, or (ii) of the primary motor type, i.e. with abnormal ipsilateral cortico-spinal projections to the paretic hand.

Brain circuits involved in emotional learning in antisocial behavior and social phobia in humans

While psychopaths (PP) lack anticipatory fear, social phobics (SP) are characterized by excessive fear. Criminal PP, SP and healthy controls (HC) participated in differential aversive delay conditioning with neutral faces as conditioned (CS) and painful pressure as unconditioned stimuli. Functional magnetic resonance imaging revealed differential activation in the limbic-prefrontal circuit (orbitofrontal cortex, insula, anterior cingulate, amygdala) in the HC. By contrast, the PP displayed brief amygdala, but no further brain activation. The SP showed increased activity to the faces in the amygdala and orbitofrontal cortex already during habituation. Thus, a hypoactive frontolimbic circuit may represent the neural correlate of psychopathic behavior, whereas an overactive frontolimbic system may underly social fear.

Right-hemispheric organization of language following early left-sided brain lesions: functional MRI topography

Left-hemispheric (LH) brain lesions acquired early in life can induce language organization in the undamaged right hemisphere (RH). This study addresses the anatomical correlates of language processing in the RH of such individuals. Five hemiparetic patients with left periventricular brain lesions of pre- and perinatal origin were included, in whom fMRI during a word generation task had yielded predominantly RH activation; five age- and sex-matched healthy right-handers served as controls. The patterns of activation in the RH of patients showed a striking similarity with the LH patterns of the normal controls, and voxel-wise comparison failed to detect significant differences. This demonstrates that in patients with early LH damage, RH recruitment for language occurs in brain areas homotopic to the LH regions involved in language processing under normal circumstances.

Dynamic brain activation during processing of emotional intonation: influence of acoustic parameters, emotional valence, and sex

Appreciation of the emotional tone of verbal utterances represents an important aspect of social life. It is still unsettled, however, which brain areas mediate processing of intonational information and whether the presumed right-sided superiority depends upon acoustic properties of the speech signal. Functional magnetic resonance imaging was used to disentangle brain activation associated with (i) extraction of specific acoustic cues and (ii) detection of specific emotional states. Stimulus material comprised pairs of emotionally intonated utterances, exclusively differing either in pitch range or in the length of stressed vowels. Hemodynamic responses showed a dynamic pattern of cerebral activation including sequenced bilateral responses of various cortical and subcortical structures. Activation associated with discrimination of emotional expressiveness predominantly emerged within the right inferior parietal lobule, within the bilateral mesiofrontal cortex and--with an asymmetry toward the right hemisphere--at the level of bilateral dorsolateral frontal cortex. Lateralization did not depend upon acoustic structure or emotional valence of stimuli. These findings might prove helpful in reconciling the controversial previous clinical and experimental data.

Intracranial oscillations of cerebrospinal fluid and blood flows: analysis with magnetic resonance imaging

PURPOSE

To detect oscillations of the cerebrospinal fluid (CSF) flow related to the heartbeat and frequencies lower than 0.6 Hz and to compare these oscillations of CSF and blood flow in cerebral vessels by using echo planar imaging in real time mode. The existence of such waves has been well known but has not yet been shown by MRI.

MATERIALS AND METHODS

In a slice perpendicular to the aqueduct, CSF flow as well as CBF, could be determined in sagittal sinus, basilar artery, and capillary vessels. After Fourier analysis, four frequency bands were assigned.

RESULTS

In the very high-frequency (heart rate) range, the integrals under the CSF curves were more closely related to arterial CBF than to changes in the sinus. Also, in the high-frequency (respiration rate), low-frequency (0.05-0.15 Hz), and very-low-frequency (0.008-0.05 Hz) ranges, the integrals under the CSF curves corresponded with arterial and capillary CBF.

CONCLUSION

Slow and fast oscillations in CSF flow are detectable in healthy persons with a proportional allotment to arterial and capillary CBF.

Object-selective responses in the human motion area MT/MST

The perception of moving objects and our successful interaction with them entail that the visual system integrates shape and motion information about objects. However, neuroimaging studies have implicated different human brain regions in the analysis of visual motion (medial temporal cortex; MT/MST) and shape (lateral occipital complex; LOC), consistent with traditional approaches in visual processing that attribute shape and motion processing to anatomically and functionally separable neural mechanisms. Here we demonstrate object-selective fMRI responses (higher responses for intact than for scrambled images of objects) in MT/MST, and especially in a ventral subregion of MT/MST, suggesting that human brain regions involved mainly in the processing of visual motion are also engaged in the analysis of object shape.

Rate-dependent activation of a prefrontal-insular-cerebellar network during passive listening to trains of click stimuli: an fMRI study

Eight volunteers underwent fMRI during passive listening to click trains. Using a parametric approach, rate-response profiles across the frequency band considered (2-6 Hz) were determined. Several cerebral structures outside the central-auditory pathways and target areas displayed distinct activation patterns each: rate-response profiles resembling high-pass (left side) or low-pass filtered (right side) signal series emerged at the level of the anterior insula, band-pass like characteristics (center frequency: 3-4 Hz) were observed within the left inferior frontal gyrus, and click train rates > 4 Hz yielded enhanced activation of the right cerebellar hemisphere. A variety of clinical and experimental data indicate that the left and right cerebral hemispheres act as high- and low-pass filters, respectively, on auditory input (double filtering by frequency theory). In light of the present fMRI data, the anterior insula contributes to the assumed double filtering by frequency functions. Furthermore, these intrasylvian areas seem to join up with the right cerebellum and the left inferior frontal gyrus to a network subserving parsing/timing functions within the auditory-verbal domain.

Activation of right fronto-temporal cortex characterizes the 'living' category in semantic processing

It is a vital ability for humans to distinguish between living and non-living objects. Whether the semantic features of these two classes of objects are represented in distinct brain areas, is unknown. In our study, words belonging to the categories 'living' and 'non-living' were presented visually to twelve right-handed volunteers, while brain activation was measured with event-related fMRI. Subjects had to judge whether the item belonged to one of these categories. Common areas of activation (P<0.05, corrected) during processing of both categories include the inferior occipital gyri bilaterally (BA 17/18), left inferior frontal gyrus (BA 44/45) and left inferior parietal lobe (BA 40). During processing of 'living' minus 'non-living' items, signal changes (P<0.05, corrected) were present in the the right inferior frontal (BA 47), middle temporal (BA 21) and fusiform gyrus (BA 19). Our results are in line with findings from patients with a deficit in semantic processing of living things, who specifically suffer from right hemispheric lesions.

The influence of current direction on phosphene thresholds evoked by transcranial magnetic stimulation

OBJECTIVES

To quantify phosphene thresholds evoked by transcranial magnetic stimulation (TMS) in the occipital cortex as a function of induced current direction.

METHODS

Phosphene thresholds were determined in 6 subjects. We compared two stimulator types (Medtronic-Dantec and Magstim) with monophasic pulses using the standard figure-of-eight coils and systematically varied hemisphere (left and right) and induced current direction (latero-medial and medio-lateral). Each measurement was made 3 times, with a new stimulation site chosen for each repetition. Only those stimulation sites were investigated where phosphenes were restricted to one visual hemifield. Coil positions were stereotactically registered. Functional magnetic resonance imaging (fMRI) of retinotopic areas was performed in 5 subjects to individually characterize the borders of visual areas; TMS stimulation sites were coregistered with respect to visual areas.

RESULTS

Despite large interindividual variance we found a consistent pattern of phosphene thresholds. They were significantly lower if the direction of the induced current was oriented from lateral to medial in the occipital lobe rather than vice versa. No difference with respect to the hemisphere was found. Threshold values normalized to the square root of the stored energy in the stimulators were lower with the Medtronic-Dantec device than with the Magstim device. fMRI revealed that stimulation sites generating unilateral phosphenes were situated at V2 and V3. Variability of phosphene thresholds was low within a cortical patch of 2x2cm(2). Stimulation over V1 yields phosphenes in both visual fields.

CONCLUSIONS

The excitability of visual cortical areas depends on the direction of the induced current with a preference for latero-medial currents. Although the coil positions used in this study were centered over visual areas V2 and V3, we cannot rule out the possibility that subcortical structures or V1 could actually be the main generator for phosphenes.

Differential activation in parahippocampal and prefrontal cortex during word and face encoding tasks

Episodic encoding is the first step in the formation of a memory trace. The relation between type of stimulus material and regional brain activation is not fully understood. We measured brain activation using fMRI in 12 healthy subjects during two experiments, word and face encoding. A widespread network of common activations in both tasks was present in the bilateral frontal (BA44/45), occipital (BA17/18/19) and fusiform gyri (BA37) as well as the right hippocampal formation (BA30). A region-of-interest-analysis for the hippocampal formation and dorsolateral prefrontal cortex (DLPFC) was performed additionally. During face encoding the right dorsal and during word encoding the bilateral ventral hippocampal region was activated. In the prefrontal cortex a lateralization to the left side was present only for word encoding. During encoding, activation in the inferior frontal and hippocampal cortex is modulated by the type of stimulus material.

Early left periventricular brain lesions induce right hemispheric organization of speech

Right-hemispheric organization of speech has been observed following early left-sided brain lesions involving the language cortex. The authors studied speech organization in hemiparetic patients with pre- and perinatally acquired lesions in the left periventricular white matter using fMRI, and found that right-hemisphere activation correlated with left facial motor tract involvement. This suggests that the impairment of speech motor output from the left hemisphere plays an important role in this alteration of language representation.

Sensorimotor mapping of the human cerebellum: fMRI evidence of somatotopic organization

Functional magnetic resonance imaging (fMRI) was employed to determine areas of activation in the cerebellar cortex in 46 human subjects during a series of motor tasks. To reduce the variance due to differences in individual anatomy, a specific transformational procedure for the cerebellum was introduced. The activation areas for movements of lips, tongue, hands, and feet were determined and found to be sharply confined to lobules and sublobules and their sagittal zones in the rostral and caudal spino-cerebellar cortex. There was a clear symmetry mirroring at the midline. The activation mapped as two distinct homunculoid representations. One, a more extended representation, was located upside down in the superior cerebellum, and a second one, doubled and smaller, in the inferior cerebellum. The two representations were remarkably similar to those proposed by Snider and Eldred [1951] five decades ago. In the upper representation, an intralimb somatotopy for the right elbow, wrist, and fingers was revealed. The maps seem to confirm earlier electrophysiological findings of sagittal zones in animals. They differ, however, from micromapping reports on fractured somatotopic maps in the cerebellar cortex of mammals. We assume that the representations that we observed are not solely the result of spatial integration of hemodynamic events underlying the fMRI method and may reflect integration of afferent peripheral and central information in the cerebellar cortex.

Are emotions contagious? Evoked emotions while viewing emotionally expressive faces: quality, quantity, time course and gender differences

In human interactions, frequently one individual becomes 'infected' with emotions displayed by his or her partner. We tested the predictions by Hatfield et al. (1992) (Primitive emotional contagion. Review of Personal and Social Psychology 14, 151-177) that the automatic, mostly unconscious component of this process, called 'primitive emotional contagion', is repeatable and fast, that stronger facial expressions of the sender evoke stronger emotions in the viewer and that women are more susceptible to emotional contagion than men. We presented photos from the Pictures of Facial Affect (Ekman and Friesen, 1976). (Pictures of Facial Affect. Consulting Psychologists Press, Palo Alto) on a PC varying the affective content (happy and sad), the expressive strength and the duration of presentation. After each photo, subjects rated the strength of experienced happiness, sadness, anger, disgust, surprise, fear and pleasure. Feelings of happiness or sadness were significantly, specifically and repeatedly evoked in the viewer - even with presentations lasting only 500 ms. Stronger expressions evoked more emotion. The gender of the viewer had weak effects. We hypothesize that this fast and repeatable reaction is likely to have a 'prewired' neural basis. We propose that the induction of emotional processes within a subject by the perception of emotionally expressive faces is a powerful instrument in the detection of emotional states in others and as the basis for one's own reactions. Detailed knowledge of emotional reactions to faces is also valuable as a basis for psychiatric studies of disorders in affect and/or communication and in studies using functional imaging (fMRI or PET) where faces are increasingly used as stimuli.