Dissociating the spatio-temporal characteristics of cortical neuronal activity associated with human volitional swallowing in the healthy adult brain

Human swallowing represents a complex highly coordinated sensorimotor function whose functional neuroanatomy remains incompletely understood. Specifically, previous studies have failed to delineate the temporo-spatial sequence of those cerebral loci active during the differing phases of swallowing. We therefore sought to define the temporal characteristics of cortical activity associated with human swallowing behaviour using a novel application of magnetoencephalography (MEG). In healthy volunteers (n = 8, aged 28-45), 151-channel whole cortex MEG was recorded during the conditions of oral water infusion, volitional wet swallowing (5 ml bolus), tongue thrust or rest. Each condition lasted for 5 s and was repeated 20 times. Synthetic aperture magnetometry (SAM) analysis was performed on each active epoch and compared to rest. Temporal sequencing of brain activations utilised time-frequency wavelet plots of regions selected using virtual electrodes. Following SAM analysis, water infusion preferentially activated the caudolateral sensorimotor cortex, whereas during volitional swallowing and tongue movement, the superior sensorimotor cortex was more strongly active. Time-frequency wavelet analysis indicated that sensory input from the tongue simultaneously activated caudolateral sensorimotor and primary gustatory cortex, which appeared to prime the superior sensory and motor cortical areas, involved in the volitional phase of swallowing. Our data support the existence of a temporal synchrony across the whole cortical swallowing network, with sensory input from the tongue being critical. Thus, the ability to non-invasively image this network, with intra-individual and high temporal resolution, provides new insights into the brain processing of human swallowing.

Co-registration of magnetoencephalography with magnetic resonance imaging using bite-bar-based fiducials and surface-matching

OBJECTIVE

To introduce a new technique for co-registration of Magnetoencephalography (MEG) with magnetic resonance imaging (MRI). We compare the accuracy of a new bite-bar with fixed fiducials to a previous technique whereby fiducial coils were attached proximal to landmarks on the skull.

METHODS

A bite-bar with fixed fiducial coils is used to determine the position of the head in the MEG co-ordinate system. Co-registration is performed by a surface-matching technique. The advantage of fixing the coils is that the co-ordinate system is not based upon arbitrary and operator dependent fiducial points that are attached to landmarks (e.g. nasion and the preauricular points), but rather on those that are permanently fixed in relation to the skull.

RESULTS

As a consequence of minimizing coil movement during digitization, errors in localization of the coils are significantly reduced, as shown by a randomization test. Displacement of the bite-bar caused by removal and repositioning between MEG recordings is minimal ( approximately 0.5 mm), and dipole localization accuracy of a somatosensory mapping paradigm shows a repeatability of approximately 5 mm. The overall accuracy of the new procedure is greatly improved compared to the previous technique.

CONCLUSIONS

The test-retest reliability and accuracy of target localization with the new design is superior to techniques that incorporate anatomical-based fiducial points or coils placed on the circumference of the head.

Receiver operating characteristic curve analysis of BMI and percentage body fat in type 2 diabetics of Punjab

The present study attempted to establish appropriate cut off levels of Body Mass Index (BMI) for defining overweight as a risk for the development of type 2 diabetes considering percentage body fat (BF) as standard. A total of 300 patients of known type 2 diabetes participated in the study (150 males and 150 females, all > or = 40 years of age). Clinical examination was done. Anthropometric measurements as BMI, Waist Circumference (WC) and Waist-hip ratio (WHR) were calculated. Percentage BF was calculated using skinfold thickness method from the equation of Durnin and Womersley. Mean BMI for males was 24.97 (SD 4.3) kg/m2 and for females was 27.56 (SD 5.14) kg/m2. Mean percentage BF for males was 28.19 (SD 0.74) and for females was 38.22 (SD 5.29). A comparison of BF and BMI data with various ethnic groups revealed conspicuous differences. Receiver operating characteristic (ROC) curve analysis showed a low sensitivity of conventional cut off value of BMI (25 kg/m2) in identifying subjects with overweight as compared to the cut off values based on percentage BF (males > 25, females > 30). This results in substantial misclassification. Based on the ROC curve, a lower cut off value of BMI 22.3 kg/m2, displayed the optimal sensitivity and specificity, and less misclassification in identification of type 2 diabetics with high percentage BF. BF: BMI was calculated and was found to be higher in females.

Acanthamoeba adherence to soft contact lens and human corneal stroma

In the present study, the adhesibility of Acanthamoeba castellani trophozoites and cysts to hydrogel contact lenses and to human cornea was investigated. Segments of unworn contact lenses were prepared (120 segments in total). In addition, 8 corneal buttons were obtained from 8 enucleated eyes. And each cornea cut into 8 radial segments. To these lens and corneal segments, 1.2 x 106/ml and 1.3 x 106/ml of cysts and trophozoites respectively were added under varying conditions. The adhesion was checked at 0, 3 and 24 hours after the exposure. Adhesion analysis showed that the trophozoites adhered equally well to lens or cornea. There is an increase in the number of trophozoites adhering to contact lenses as well as cornea. This difference is more significant for contact lenses. Washing of contact lenses significantly decreased the adherence of the trophozoites after 3 hours of incubation. When the comparison of adhesion was done between the unwashed worn and unwashed unworn contact lenses, it was observed that there was a significant difference in adherence to new lenses where the adherence was much lower. The study shows that washing of contact lenses does decrease the chances of colonization by Acantamoeba catellani and also that older lenses have higher chances of getting colonized probably due to the occurrence of scratches et. on the surface which may help in colonization.

Estimating receptive field size from fMRI data in human striate and extrastriate visual cortex

Functional magnetic resonance imaging (fMRI) was used to estimate the average receptive field sizes of neurons in each of several striate and extrastriate visual areas of the human cerebral cortex. The boundaries of the visual areas were determined by retinotopic mapping procedures and were visualized on flattened representations of the occipital cortex. Estimates of receptive field size were derived from the temporal duration of the functional activation at each cortical location as a visual stimulus passed through the receptive fields represented at that location. Receptive fields are smallest in the primary visual cortex (V1). They are larger in V2, larger again in V3/VP and largest of all in areas V3A and V4. In all these areas, receptive fields increase in size with increasing stimulus eccentricity. The results are qualitatively in line with those obtained by others in macaque monkeys using neurophysiological methods.

An fMRI study of stimulus equivalence

In order to study brain activation during the formation of equivalence relations, 12 subjects underwent fMRI during matching-to-sample (MTS) tests of (1) previously trained arbitrary relationships between iconic stimuli and the untrained, emergent relations of (2) symmetry, (3) transitivity, and (4) symmetry with transitivity, plus a test of verbal fluency (VF). Brain activation was similar in all MTS tasks and in the VF task. In particular, both types of task activated dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex bilaterally. However VF, but not the MTS tasks, activated Broca's area. In three of the four MTS tasks, behavioural accuracy was significantly correlated with left lateralisation of DLPFC activity. Brain activation patterns during equivalence thus resembled those involved in semantic processing underlying language, without involving regions concerned with the simple sub-vocal articulation of stimulus names.

Spatiotemporal frequency and direction sensitivities of human visual areas measured using fMRI

Using functional magnetic resonance imaging (fMRI) we have studied the variation in response magnitude, in each visual area (V1-V5), as a function of spatial frequency (SF), temporal frequency (TF) and unidirectional motion versus counterphase flicker. Each visual area was identified in each subject using a combination of retinotopic mapping fMRI and cortical flattening techniques. A drifting (or counterphasing) sinusoidal grating was used as the stimulus in a study in which we parametrically varied SF between 0.4 and 7 cycles/degree and TF between 0 and 18 Hz. For each experiment we constructed fMRI amplitude tuning curves, averaged across subjects, for each visual area. The tuning curves that resulted are consistent with the known physiological properties of cells in the corresponding macaque visual areas, previous functional imaging studies, and in the case of V1, the psychophysically determined contrast sensitivity functions for spatial and temporal frequency. In the case of V3A, the SF tuning functions obtained were more similar to those found in single cell studies of macaque V3 rather than macaque V3A. All areas showed at least a moderate preference for directed versus counterphasing motion with V5 showing the largest preference. Visual areas V1, V2, V3, and V3A showed more direction sensitivity at low spatial frequencies, while VP, V4, and V5 had the highest drifting versus counterphasing ratios for higher spatial frequencies.

Effect of Giardia lamblia on duodenal disaccharidase levels in humans

The study was conducted to detect the effect of giardiasis on human disaccharidase levels. Forty patients attending the medical outpatient department of PGIMER, Chandigarh were enrolled. Twenty patients, positive for Giardia lamblia comprised the study group while 20 patients negative for Giardia lamblia were taken as controls. Upper gastrointestinal endoscopy was performed in all patients. Estimation of lactase, sucrase, maltase and trehalase was done in biopsies. Histopathological investigation was carried out in all biopsy specimens after Haematoxylin and Eosin staining. Complaints of pain abdomen and bloating occurred commonly in giardiasis. Four biopsy samples in study group showed mild increase in lymphomononuclear infiltrate. Giardia lamblia was detected in 7 biopsies. Lactase levels were decreased significantly (p < 0.05) in giardiasis. Rest of the enzymes were comparable to the controls. No differences in the enzyme activities were observed between males and females in either group and with the duration of symptoms.

Global motion adaptation

Image motion is initially detected locally. Local motion signals are then integrated across space in order to specify the global motion of objects or surfaces. It is well known that prolonged exposure to motion causes adaptation at the local motion level. We have investigated whether adaptation also occurs at the global motion level. We have devised a global motion stimulus (a random dot kinematogram) which has equal motion energy in opposite directions but nonetheless gives rise to global motion perception. At the local motion level, adaptation to this stimulus should cause equal adaptation in both directions and should not give rise to an aftereffect. Any aftereffect seen must therefore be attributable to adaptation at the global motion level. We find that following adaptation to this stimulus, judgements of the perceived direction of a test pattern are systematically biased towards the direction opposite to the adapting direction, suggesting that adaptation does occur at a level of visual processing at which global motion is represented.

Attentional suppression of activity in the human visual cortex

We have used fMRI to examine the nature of the changes that occur in the human visual cortex when an observer attends to a particular location in the visual image. Previous studies have shown that the magnitude of the response to a visual stimulus is increased when the observer attends to the stimulus. We show that, in addition, attention to a particular location results in a widespread suppression of activity levels at all other locations. This suggests that a key mechanism of attentional modulation may be that spontaneous (baseline) levels of neural activity are adjusted in a position-dependent manner across the entire visual field.

The cortical topography of human anorectal musculature

BACKGROUND & AIMS

The muscles of the anorectum are important in the volitional control of continence, yet virtually no information exists on their cortical representation in humans.

METHODS

Topographic cortical mapping of both cerebral hemispheres was performed in 9 healthy subjects by applying suprathreshold transcranial magnetic stimulation to individual points on a scalp grid centered over the vertex and then recording the electromyographic responses from the external anal sphincter, rectum, and tibialis anterior muscles.

RESULTS

Cortically evoked anal and rectal response latencies were similar (20.2 +/- 1.7 and 19.8 +/- 1.5 milliseconds, respectively) and were shorter than those from the anterior tibialis muscle (right, 29.7 +/- 2.3 milliseconds; left, 29.9 +/- 1.8 milliseconds; P < 0.0005). Cortical mapping showed that the anal responses were bilaterally represented on the superior motor cortex (Brodmann area 4) of both cerebral hemispheres; a similar topography was found for the rectal responses. By comparison, the tibialis responses showed predominantly contralateral medial motor cortex representation. Subtle but consistent differences in the degree of bilateral hemispheric representation were also apparent both between and within individuals for the anal responses and to a lesser extent for the rectal responses.

CONCLUSIONS

The anorectal musculature has bilateral motor cortex representation with similar topography, but there is intersubject variation in the degree of symmetry.

Recovery of swallowing after dysphagic stroke relates to functional reorganization in the intact motor cortex

BACKGROUND & AIMS

The aim of this study was to determine the mechanism for recovery of swallowing after dysphagic stroke.

METHODS

Twenty-eight patients who had a unilateral hemispheric stroke were studied 1 week and 1 and 3 months after the stroke by videofluoroscopy. Pharyngeal and thenar electromyographic responses to magnetic stimulation of multiple sites over both hemispheres were recorded, and motor representations were correlated with swallowing recovery.

RESULTS

Dysphagia was initially present in 71% of patients and in 46% and 41% of the patients at 1 and 3 months, respectively. Cortical representation of the pharynx was smaller in the affected hemisphere (5 +/- 1 sites) than the unaffected hemisphere (13 +/- 1 sites; P </= 0.001). Nondysphagic and persistently dysphagic patients showed little change in pharyngeal representation in either hemisphere at 1 and 3 months compared with presentation, but dysphagic patients who recovered had an increased pharyngeal representation in the unaffected hemisphere at 1 and 3 months (15 +/- 2 and 17 +/- 3 vs. 9 +/- 2 sites; P </= 0.02) without change in the affected hemisphere. In contrast, thenar representation increased in the affected hemisphere but not the unaffected hemisphere at 1 and 3 months (P </= 0.01).

CONCLUSIONS

Return of swallowing after dysphagic stroke is associated with increased pharyngeal representation in the unaffected hemisphere, suggesting a role for intact hemisphere reorganization in recovery.

Co-registration of cortical magnetic stimulation and functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) are noninvasive techniques recently used to investigate cortical motor physiology. However, these modalities measure different phenomena, and in studies of human motor control they have given inconsistent results. We have developed a reproducible technique which co-registers TMS and fMRI, using a frameless method. In four normal subjects, the TMS map and fMRI activation were present on the primary motor cortex contralateral to the target hand, with some extension into primary sensory cortex. fMRI activation alone was also present in the medial motor cortex bilaterally and in the sensorimotor cortex ipsilateral to the target hand. This technique allows a more comprehensive evaluation of the physiologic events involved in motor control.

Efficacy of milk versus yogurt offered as part of a mixed diet in acute noncholera diarrhea among malnourished children

We compared the clinical outcome of acute diarrhea in 96 malnourished boys (aged 4 to 47 months) receiving full-strength milk compared with yogurt offered as part of a mixed diet. All had weight for height less than or equal to 80% of the National Centre for Health Statistics median. They were randomly assigned to receive milk formula (MF; 67 cal/100 ml) or yogurt formula (YF; prepared from the same milk formula) at the rate of 120 ml/kg body weight in seven divided feedings. Stool-reducing substances (> 1%) were detected more frequently in the MF group, and the differences were significant for day 3 of the study (p = 0.04). However, the geometric mean (95% confidence interval) of the total stool weights (gm/kg) during 0 to 72 hours (MF 128.8 [103, 161.4]; YF 110.9 [87, 142.2]) was comparable (p = 0.37) as was the median (range) duration of diarrhea (hours) (MF 45 [4, 183]; YF 52 [7, 173] p = 0.94). The treatment failure rates in the MF (8.2%) and YF (6.3%) groups were also similar (p = 0.67). The children consuming milk had higher median percent weight gain at the end of 72 hours of the study (p = 0.04) and at recovery (p = 0.02). Routine substitution of yogurt as small frequent feedings as an addition for semisolid food to malnourished children with acute diarrhea does not achieve any significant clinical benefit versus milk.

The processing of first- and second-order motion in human visual cortex assessed by functional magnetic resonance imaging (fMRI)

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significantly greater for second-order motion than for first-order motion. This trend is evident, but less marked, in V3A and V3B and absent in V5. The results are consistent with the hypothesis that first-order motion sensitivity arises in V1, that second-order motion is first represented explicitly in V3 and VP, and that V5 (and perhaps also V3A and V3B) is involved in further processing of motion information, including the integration of motion signals of the two types.

Long-term reorganization of human motor cortex driven by short-term sensory stimulation

Removal of sensory input can induce changes in cortical motor representation that reverse when sensation is restored. Here we ask whether manipulation of sensory input can induce long-term reorganization in human motor cortex that outlasts the initial conditioning. We report that for at least 30 minutes after pharyngeal stimulation, motor cortex excitability and area of representation for the pharynx increased, while esophagus representation decreased, without parallel changes in the excitability of brainstem-mediated reflexes. Therefore increased sensory input can drive long-term cross-system changes in motor areas of the cerebral cortex, which suggests that sensory stimulation might rehabilitate dysphagia, a frequent consequence of cerebral injury.

Cortical localisation of magnetic fields evoked by oesophageal distension

Magnetoencephalographic source localisation techniques were used to measure oesophageal evoked magnetic fields from the cerebral cortex in 3 subjects. By using rapid balloon distension as a stimulus, a comparison of proximal and distal oesophageal cortical representation was made. The distal oesophagus was represented bilaterally in the insular cortex and SII as well as the inferior aspect of SI. The proximal oesophagus was represented unilaterally in superior and inferior SI, insular cortex and SII. Significantly, the superior portion of SI was consistently activated in subjects following stimulation of the proximal oesophagus, but similar activation was not found in response to distal stimulation. This may reflect the contribution from somatic afferent fibres in the striate muscle of the proximal segment. In conclusion, vagal afferents appear to contribute more to cortical activation following stimulation of the distal rather than the proximal oesophagus, while spinal afferents appear to be activated by both proximal and distal oesophageal stimulation.

Topographic mapping of trans-cranial magnetic stimulation data on surface rendered MR images of the brain

We present a method for the coregistration and topographic mapping of trans-cranial magnetic stimulation (TCMS) data on surface rendered images of the cortex, derived from Magnetic Resonance Images (MRI). We describe the TCMS procedure and the methods used to locate the TCM stimulation sites in the MRI coordinate system, and the algorithms needed to depict the TCMS distribution as a pseudocolour contour map on the cortical surface. The methods are validated using TCMS data from the hand (thenar) and leg (tibialis muscle). The methods used correctly depict the expected motor representations of each of these areas and we therefore propose that this technique may be used as a functional imaging tool in the investigation of cortical function in both normals and patients.

Higher-Order Motion Perception in Human Visual Cortex: Evidence from fMRI

fMRI was used to investigate human visual cortex responses to higher-order motion stimuli. Acquisition was on a Siemens 1.5 T scanner (T2*, gradient-recalled EPI, TR 3000 ms, TE 84 ms, flip angle 90°, 2 mm × 2 mm voxels, 256 mm FOV, 10 4-mm slices, 54 acquisitions per run). The measured volume included occipital and posterior parietal cortex. T1 scouts and, in some subjects, high resolution T1 volume images were also acquired. Visual stimuli were gamma-corrected movies (480 × 480 pixels), presented by a PowerMac via an LCD projector, shown through the rear of the scanner onto an adjustable mirror fixed above the subject's eyes. Three types of stimuli were used: (1) first-order motion, (2) second-order motion (both radial sine waves on random-dot backgrounds), (3) structure-from-motion consisting of two rotating circular patches (5 deg diameter) within which dots moved in a constant (centripetal) direction, superimposed on randomly moving dots. Three interleaved comparisons were made: stimulus vs blank, first-order vs second-order, and random motion vs structure-from-motion (27 s each phase, 3 repeats).

Analysis was based on a correlation coefficient method, after head-motion correction. Initial correlation was with the stimulus profile vector, then with an average BOLD response vector. Voxels with a correlation >0.5 (p<0.0003) were accepted as significant. In all subjects (seven- teen normals), all stimuli evoked bilateral activity in V1/V2 (BA17/18), and in extrastriate area V5/MT (BA37/19). Bilateral activation was also found in areas V3/V3a (BA19) and BA7. A more pronounced activation of area MST/V5a (BA37/39) was found in response to the structure-from-motion stimulus, compared with random motion.[Supported by: Wellcome Trust, Schilling Foundation.]

Magnetoencephalographic investigation of human cortical area V1 using color stimuli

The aim of this study was to determine the response properties of the human visual cortex to chromatic stimuli using magnetoencephalography (MEG). Evoked responses were recorded to isoluminant red/green sinusoidal gratings for a wide range of spatial and temporal frequencies. For each condition the response was dominated by a single major component which was well modeled by an equivalent current dipole. Coregistration of MEG and MRI data provided evidence that the principal evoked cortical activity originated from visual area V1. To investigate the chromatic response properties of this area, the maximum global field power of the evoked response was plotted as a function of stimulus spatial and temporal frequency. The spatial-frequency tuning was lowpass and the temporal-frequency tuning was multimodal, with peaks at 0 and 4 Hz. The results demonstrate the use of MEG as a technique for investigating activity from discrete regions of cortex.

Evaluation of MRI-MEG/EEG co-registration strategies using Monte Carlo simulation

We present a Monte Carlo analysis method for evaluating MRI-MEG/EEG co-registration techniques. The method estimates the error in co-registration as a function of position within the brain. Using this analysis technique, we demonstrate the limitations of conventional head-based fiducial point methods, and propose a new strategy utilising a dental bite-bar incorporating accurately machined fiducial markers. Results presented demonstrate the improved accuracy of MEG/EEG to MRI co-registration using the bite-bar.

Efficacy of milk-based diets in persistent diarrhea: a randomized, controlled trial

OBJECTIVE

Previous studies have shown increased stool output when children with persistent diarrhea (PD) received milk as the predominant source of nutrition.

METHODS

We evaluated the efficacy of milk given in modest amounts as a part of a mixed diet in children with PD. One hundred sixteen children 3 to 24 months of age with diarrhea for between 14 days and 12 weeks were allocated to milk-based (n = 60) or milk-free (n = 56) cereal dietary regimens. The two diets were isocaloric (86.9 calories/100 g for < or = 9 months; 95.6 cal/100 g for > 9 months) consisting of puffed rice cereal, sugar, and oil differing in only their source of protein, which was either milk or egg white, respectively. An average of 30% of the calories were constituted by milk in the milk-cereal diet. Both diets were offered at the rate of 150 kcal/kg per day. Children receiving milk-cereal consumed an average of 1.9 g/kg lactose per day.

RESULTS

The baseline characteristics in the two groups were similar. Comparable amounts of diet were consumed in both groups. The milk-cereal group did not have higher median (range) stool output (g/kg/h) compared with the milk-free group during a 0- to 48-hour (milk-cereal, 1.7 [0.2 to 8.7]; milk-free, 1.5 [0.1 to 6.6]) or 0- to 120-hour (milk-cereal, 1.6 [0.4 to 7.2]; milk-free, 1.3 [0.1 to 7.6]) period. The percentage of weight gain was similar in the two groups, and there were no significant differences in the duration of diarrhea. Overall, 23 children had treatment failures, 10 (17%) in the milk-cereal and 13 (23.6%) in the milk-free groups.

CONCLUSIONS

Our findings suggest that modest intakes of milk are well tolerated as a part of mixed diet during PD.

The cortical topography of human swallowing musculature in health and disease

Because no detailed information exists regarding the topographic representation of swallowing musculature on the human cerebral cortex in health or disease, we used transcranial magnetic stimulation to study the cortical topography of human oral, pharyngeal and esophageal musculature in 20 healthy individuals and the topography of pharyngeal musculature in two stroke patients, one with and one without dysphagia. Our results demonstrate that swallowing musculature is discretely and somatotopically represented on the motor and premotor cortex of both hemispheres but displays interhemispheric asymmetry, independent of handedness. Following stroke, dysphagia appeared to be associated with smaller pharyngeal representation on the intact hemisphere, which increases in size with recovery of swallowing.