Biomedical subjects

J Driver

Publications and source records attributed to J Driver.

At least 19 recordsLinked to original sources

PubMed2006

Reversible reproductive control in harbour seals (Phoca vitulina) with a gonadotropin-releasing hormone agonist.

Reproductive control in captive pinnipeds is an important management subject for many facilities. To date reproductive control in harbour seals (Phoca vitulina) has been achieved using anti-androgens, progestagen preparations, castration, and physical separation of the sexes. The harbour seal group at the seal station in Friedrichskoog, Germany consists of three mature females (all >10 years), one older mature male (13 years of age in 2000) and one male who reached maturity during the study (3 years of age in 2000). In 2000 the older mature male received for the first time a 3-month depot injection of a gonadotropin-releasing hormone agonist (buserelin acetetate, 9.9 mg) by subcutaneous injection. This male was subsequently given the gonadotropin-releasing hormone agonist in 2001, 2004 and 2005. The younger male reached maturity during the investigation and received burserelin for the first time in 2004 and again in 2005. No pups were born in 2001, 2002, 2005 or 2006. No reproductive control was performed in 2002 and 2003, resulting in three newborns in 2003 and 2004. Serum levels of testosterone were measured by a routine liquid chromatography coupled with mass spectometry. Pre-burserelin testosterone levels varied between 0.02 and 2.18 ng/ml. Post-burserelin levels were under the detection limit except for the first year of the investigation. No behavioural changes such as changes in social ranking and no clinical side effects were observed. This study shows that the gonadotropin-releasing hormone agonist, burserelin acetate, can be used for reversible reproductive control in harbour seals without observed side effects or detrimental behavioural changes.

Animals↗

PubMed2006

Mechanisms of top-down facilitation in perception of visual objects studied by FMRI.

Prior knowledge regarding the possible identity of an object facilitates its recognition from a degraded visual input, though the underlying mechanisms are unclear. Previous work implicated ventral visual cortex but did not disambiguate whether activity-changes in these regions are causal to or merely reflect an effect of facilitated recognition. We used functional magnetic resonance imaging to study top-down influences on processing of gradually revealed objects, by preceding each object with a name that was congruent or incongruent with the object. Congruently primed objects were recognized earlier than incongruently primed, and this was paralleled by shifts in activation profiles for ventral visual, parietal, and prefrontal cortices. Prior to recognition, defined on a trial-by-trial basis, activity in ventral visual cortex rose gradually but equivalently for congruently and incongruently primed objects. In contrast, prerecognition activity was greater with congruent priming in lateral parietal, retrosplenial, and lateral prefrontal cortices, whereas functional coupling between parietal and ventral visual (and also left lateral prefrontal and parietal) cortices was enhanced in the same context. Thus, when controlling for recognition point and stimulus information, activity in ventral visual cortex mirrors recognition success, independent of condition. Facilitation by top-down cues involves lateral parietal cortex interacting with ventral visual areas, potentially explaining why parietal lesions can lead to deficits in recognizing degraded objects even in the context of top-down knowledge.

Adult↗

PubMed2006

Cortical correlates of TMS-induced phantom hand movements revealed with concurrent TMS-fMRI.

We studied an amputee patient who experiences a conscious sense of movement (SoM) in her phantom hand, without significant activity in remaining muscles, when transcranial magnetic stimulation (TMS) is applied at appropriate intensity over the corresponding sector of contralateral motor cortex. We used the novel methodological combination of TMS during fMRI to reveal the neural correlates of her phantom SoM. A critical contrast concerned trials at intermediate TMS intensities: low enough not to produce overt activity in remaining muscles; but high enough to produce a phantom SoM on approximately half such trials. Comparing trials with versus without a phantom SoM reported phenomenally, for the same intermediate TMS intensities, factored out any non-specific TMS effects on brain activity to reveal neural correlates of the phantom SoM itself. Areas activated included primary motor cortex, dorsal premotor cortex, anterior intraparietal sulcus, and caudal supplementary motor area, regions that are also involved in some hand movement illusions and motor imagery in normals. This adds support to proposals that a conscious sense of movement for the hand can be conveyed by activity within corresponding motor-related cortical structures.

Adult↗

PubMed2005

Multisensory stimulation with or without saccades: fMRI evidence for crossmodal effects on sensory-specific cortices that reflect multisensory location-congruence rather than task-relevance.

During covert attention to peripheral visual targets, presenting a concurrent tactile stimulus at the same location as a visual target can boost neural responses to it, even in sensory-specific occipital areas. Here, we examined any such crossmodal spatial-congruence effects in the context of overt spatial orienting, when saccadic eye-movements were directed to each peripheral target or central fixation maintained. In addition, we tested whether crossmodal spatial-congruence effects depend on the task-relevance of visual or tactile stimuli. On each trial, subjects received spatially congruent (same location) or incongruent (opposite hemifields) visuo-tactile stimulation. In different blocks, they made saccades either to the location of each visual stimulus, or to the location of each tactile stimulus; or else passively received the multisensory stimulation. Activity in visual extrastriate areas and in somatosensory parietal operculum was modulated by spatial congruence of the multisensory stimulation, with stronger activations when concurrent visual and tactile stimuli were both delivered at the same contralateral location. Critically, lateral occipital cortex and parietal operculum showed such crossmodal spatial effects irrespective of which modality was task relevant; and also of whether the stimuli were used to guide eye-movements or were just passively received. These results reveal crossmodal spatial-congruence effects upon visual and somatosensory sensory-specific areas that are relatively 'automatic', determined by the spatial relation of multisensory input rather than by its task-relevance.

Adolescent↗

PubMed2004

Influence of gaze direction on crossmodal modulation of visual ERPS by endogenous tactile spatial attention.

Recent evidence indicates that the spatial direction of endogenous covert spatial attention in one sensory modality can crossmodally influence early processing of stimuli in a different modality. However, spatial locations are initially coded according to different frames of reference for different modalities (e.g., body-centered for touch versus retinocentric vision) and postural changes (e.g., gaze shifts) will realign these. Here, we used event-related potentials (ERPs) to investigate how the direction of endogenous tactile attention affects sensory-specific visual ERP components. Critically, by manipulating direction of gaze, we were able to test whether any crossmodal effects depend on visual and tactile projections to a common hemisphere, on common locations in external space, or on some combination of the two. We found that both P1 and N1 visual components were modulated according to the direction of endogenous tactile attention. While the P1 crossmodal effect followed purely hemispheric constraints, the attentional modulation of N1 appeared to combine both anatomical and external spatial constraints.

Adult↗

PubMed2004

Results of a technology demonstration project to compare rapid aquatic toxicity screening tests in the analysis of industrial effluents.

The results of a 'BioWise' demonstration project to assess the comparative sensitivity and practicality of seven new assays for the direct assessment of ecotoxicity in industrial effluents are presented. In addition the aim of the project was to validate the results of the new assays against benchmark data generated from non-proprietary, rapid, microplate screening assays using the regulatory species; freshwater crustacean Daphnia magna and green algae Selenastrum capricornutum, chosen in view of their environmental relevance. The new commercial test assays were: Daphnia magna, Selenastrum capricornutum and Thamnocephalus platyurus Toxkits supplied by Vickers Laboratories Ltd, containing dormant, immobilised life stages of the test species; GreenScreen EM, a yeast based assay for genotoxicity and general acute toxicity supplied by Gentronix Ltd; and CellSense a mediated, amperometric whole cell biosensor based on immobilised activated sludge and E. coli. 38 effluent samples supplied by members of SOCSA (Specialised Organic Chemicals Sector Association) were examined over a period of 13 months, in the project co-ordinated by the AstraZeneca Brixham Environmental Laboratory, and part funded by BioWise via the UK Government Department of Trade and Industry.

Animals↗

PubMed2004

BOLD repetition decreases in object-responsive ventral visual areas depend on spatial attention.

Functional imaging studies of priming-related repetition phenomena have become widely used to study neural object representation. Although blood oxygenation level-dependent (BOLD) repetition decreases can sometimes be observed without awareness of repetition, any role for spatial attention in BOLD repetition effects remains largely unknown. We used fMRI in 13 healthy subjects to test whether BOLD repetition decreases for repeated objects in ventral visual cortices depend on allocation of spatial attention to the prime. Subjects performed a size-judgment task on a probe object that had been attended or ignored in a preceding prime display of 2 lateralized objects. Reaction times showed faster responses when the probe was the same object as the attended prime, independent of the view tested (identical vs. mirror image). No behavioral effect was evident from unattended primes. BOLD repetition decreases for attended primes were found in lateral occipital and fusiform regions bilaterally, which generalized across identical and mirror-image repeats. No repetition decreases were observed for ignored primes. Our results suggest a critical role for attention in achieving visual representations of objects that lead to both BOLD signal decreases and behavioral priming on repeated presentation.

Adult↗

PubMed2004

Spatial and temporal factors during processing of audiovisual speech: a PET study.

Speech perception can use not only auditory signals, but also visual information from seeing the speaker's mouth. The relative timing and relative location of auditory and visual inputs are both known to influence crossmodal integration psychologically, but previous imaging studies of audiovisual speech focused primarily on just temporal aspects. Here we used Positron Emission Tomography (PET) during audiovisual speech processing to study how temporal and spatial factors might jointly affect brain activations. In agreement with previous work, synchronous versus asynchronous audiovisual speech yielded increased activity in multisensory association areas (e.g., superior temporal sulcus [STS]), plus in some unimodal visual areas. Our orthogonal manipulation of relative stimulus position (auditory and visual stimuli presented at same location vs. opposite sides) and stimulus synchrony showed that (i) ventral occipital areas and superior temporal sulcus were unaffected by relative location; (ii) lateral and dorsal occipital areas were selectively activated for synchronous bimodal stimulation at the same external location; (iii) right inferior parietal lobule was activated for synchronous auditory and visual stimuli at different locations, that is, in the condition classically associated with the 'ventriloquism effect' (shift of perceived auditory position toward the visual location). Thus, different brain regions are involved in different aspects of audiovisual integration. While ventral areas appear more affected by audiovisual synchrony (which can influence speech identification), more dorsal areas appear to be associated with spatial multisensory interactions.

Adult↗

PubMed2004

Group study of an "undercover" test for visuospatial neglect: invisible cancellation can reveal more neglect than standard cancellation.

Visual neglect is a relatively common deficit after brain damage, particularly strokes. Cancellation tests provide standard clinical measures of neglect severity and deficits in daily life. A recent single-case study introduced a new variation on standard cancellation. Instead of making a visible mark on each target found, the patient made invisible marks (recorded with carbon paper underneath, for later scoring). Such invisible cancellation was found to reveal more neglect than cancellation with visible marks. Here we test the generality of this. Twenty three successive cases with suspected neglect each performed cancellation with visible or invisible marks. Neglect of contralesional targets was more pronounced with invisible marks. Indeed, about half of the patients only showed neglect in this version. For cases showing more neglect with invisible marks, stronger neglect of contralesional targets correlated with more revisits to ipsilesional targets for making additional invisible marks upon them. These results indicate that cancellation with invisible marks can reveal more neglect than standard cancellation with visible marks, while still providing a practical bedside test. Our observations may be consistent with recent proposals that demands on spatial working memory (required to keep track of previously found items only when marked invisibly) can exacerbate spatial neglect.

Aged↗

PubMed2003

Prism adaptation can improve contralesional tactile perception in neglect.

The authors show that prismatic adaptation can reduce tactile inattention in stroke patients with unilateral neglect. Four patients with visuospatial neglect and tactile extinction underwent 10-minute application of 20 degrees right-shifting prismatic lenses during pointing. This improved contralesional tactile perception in all patients, even for a task requiring no exploration or spatial motor responses. This finding suggests a potential role for prismatic adaptation in the rehabilitation of multiple sensory modalities in patients with neglect.

Adaptation, Physiological↗

PubMed2003

Preparatory states in crossmodal spatial attention: spatial specificity and possible control mechanisms.

We used event-related functional magnetic resonance imaging to study the neural correlates of endogenous spatial attention for vision and touch. We examined activity associated with attention-directing cues (central auditory pure tones), symbolically instructing subjects to attend to one hemifield or the other prior to upcoming stimuli, for a visual or tactile task. In different sessions, subjects discriminated either visual or tactile stimuli at the covertly attended side, during bilateral visuotactile stimulation. To distinguish cue-related preparatory activity from any modulation of stimulus processing, unpredictably on some trials only the auditory cue was presented. The use of attend-vision and attend-touch blocks revealed whether preparatory attentional effects were modality-specific or multimodal. Unimodal effects of spatial attention were found in somatosensory cortex for attention to touch, and in occipital areas for attention to vision, both contralateral to the attended side. Multimodal spatial effects (i.e. effects of attended side irrespective of task-relevant modality) were detected in contralateral intraparietal sulcus, traditionally considered a multimodal brain region; and also in the middle occipital gyrus, an area traditionally considered purely visual. Critically, all these activations were observed even on cue-only trials, when no visual or tactile stimuli were subsequently presented. Endogenous shifts of spatial attention result in changes of brain activity prior to the presentation of target stimulation (baseline shifts). Here, we show for the first time the separable multimodal and unimodal components of such preparatory activations. Additionally, irrespective of the attended side and modality, attention-directing auditory cues activated a network of superior frontal and parietal association areas that may play a role in voluntary control of spatial attention for both vision and touch.

Attention↗

PubMed2003

Parapoxvirus infection in harbor seals (Phoca vitulina) from the German North Sea.

In the summer of 2000, proliferative lesions of the skin and oral mucosa were observed in 26 young harbor seals (Phoca vitulina) from a rehabilitation center in Schleswig-Holstein, Germany. Verrucose, roundish nodules, approximately 1-2 cm in diameter, were presented in the oral cavity, especially on the tongue. Some animals developed similarly sized spherical dermal elevations with ulceration on flippers, chest, neck, and perineum. Necropsy of one animal showed multifocal, verrucose nodules in the oral cavity and a mild tonsillitis. Histologically, the nodules were characterized by ballooning degeneration of the outer parts of the spiny layer and stratum granulosum, with large eosinophilic cytoplasmic inclusions and a perivascular to interstitial lymphohistiocytic infiltration accompanied by fibroblastic proliferation and neovascularization. Negative staining of mucosal tissue homogenates demonstrated parapoxvirus-like particles. The presence of parapoxvirus was confirmed by polymerase chain reaction, using primers specific for parapoxvirus of ungulates. By in situ hybridization, using a parapox-specific, digoxigenin-labeled DNA probe, abundant parapoxvirus DNA-positive epithelial cells were detected in the stratum granulosum and the outer parts of the spiny layer. There was no parapoxvirus-positive signal in the adjacent submucosa. Although DNA analysis revealed that the causative agent can clearly be distinct from terrestrial parapoxviruses, lesions resembled parapoxvirus infections in other terrestrial species, and the pattern of virus DNA distribution indicated a direct effect of the virus on keratinocytes. In contrast, changes in the corium may be considered an indirect response mediated by the virus or the immune system.

Animals↗

PubMed2002

Crossmodal spatial influences of touch on extrastriate visual areas take current gaze direction into account.

Recent results indicate that crossmodal interactions can affect activity in cortical regions traditionally regarded as "unimodal." Previously we found that combining touch on one hand with visual stimulation in the anatomically corresponding hemifield could boost responses in contralateral visual cortex. Here we manipulated which visual hemifield corresponded to the location of the stimulated hand, by changing gaze direction such that right-hand touch could now arise in either the left or right visual field. Crossmodal effects on visual cortex switched from one hemisphere to the other, depending on gaze direction, regardless of whether the hand was seen. This indicates that crossmodal influences of touch upon visual cortex depend on spatial alignment for the multimodal stimuli, with gaze posture taken into account.

Adult↗

PubMed2002

Supramodal effects of covert spatial orienting triggered by visual or tactile events.

Event-related functional magnetic resonance imaging was used to identify brain areas involved in spatial attention and determine whether these operate unimodally or supramodally for vision and touch. On a trial-by-trial basis, a symbolic auditory cue indicated the most likely side for the subsequent target, thus directing covert attention to one side. A subsequent target appeared in vision or touch on the cued or uncued side. Invalidly cued trials (as compared with valid trials) activated the temporo-parietal junction and regions of inferior frontal cortex, regardless of target modality. These brain areas have been associated with multimodal spatial coding in physiological studies of the monkey brain and were linked to a change in the location that must be attended to in the present study. The intraparietal sulcus and superior frontal cortex were also activated in our task, again, regardless of target modality, but did not show any specificity for invalidly cued trials. These results identify a supramodal network for spatial attention and reveal differential activity for inferior circuits involving the temporo-parietal junction and inferior frontal cortex (specific to invalid trials) versus more superior intraparietal-frontal circuits (common to valid and invalid trials).

Adult↗

PubMed2002

The perception of body orientation after neck-proprioceptive stimulation. Effects of time and of visual cueing.

Different sensory systems (e.g. proprioception and vision) have a combined influence on the perception of body orientation, but the timescale over which they can be integrated remains unknown. Here we examined how visual information and neck proprioception interact in perception of the "subjective straight ahead" (SSA), as a function of time since initial stimulation. In complete darkness, healthy subjects directed a laser spot to the point felt subjectively to be exactly straight ahead of the trunk. As previously observed, left neck muscle vibration led to a disparity between subjective perception and objective position of the body midline, with SSA misplaced to the left. We found that this displacement was sustained throughout 28 min of continuous proprioceptive stimulation, provided there was no visual input. Moreover, prolonged vibration of neck muscles leads to a continuing disparity between subjective and objective body orientation even after offset of the vibration; the longer the preceding vibration, the more persistent the illusory deviation of body orientation. To examine the role of vision, one group of subjects fixated a central visual target at the start of each block of continuous neck vibration, with SSA then measured at successive intervals in darkness. The illusory deviation of SSA was eliminated whenever visual input was provided, but returned as a linear function of time when visual information was eliminated. These results reveal: the persistent effects of neck proprioception on the SSA, both during and after vibration; the influence of vision; and integration between incoming proprioceptive information and working memory traces of visual information.

Adult↗

PubMed2002

Neural response to emotional faces with and without awareness: event-related fMRI in a parietal patient with visual extinction and spatial neglect.

This study examined whether differential neural responses are evoked by emotional stimuli with and without conscious perception, in a patient with visual neglect and extinction. Stimuli were briefly shown in either right, left, or both fields during event-related fMRI. On bilateral trials, either a fearful or neutral left face appeared with a right house, and it could either be extinguished from awareness or perceived. Seen faces in left visual field (LVF) activated primary visual cortex in the damaged right-hemisphere and bilateral fusiform gyri. Extinguished left faces increased activity in striate and extrastriate cortex, compared with right houses only. Critically, fearful faces activated the left amygdala and extrastriate cortex both when seen and when extinguished; as well as bilateral orbitofrontal and intact right superior parietal areas. Comparison of perceived versus extinguished faces revealed no difference in amygdala for fearful faces. Conscious perception increased activity in fusiform, parietal and prefrontal areas of the left-hemisphere, irrespective of emotional expression; while a differential emotional response to fearful faces occurring specifically with awareness was found in bilateral parietal, temporal, and frontal areas. These results demonstrate that amygdala and orbitofrontal cortex can be activated by emotional stimuli even without awareness after parietal damage; and that substantial unconscious residual processing can occur within spared brain areas well beyond visual cortex, despite neglect and extinction.

Aged↗

PubMed2002

Multiple levels of visual object constancy revealed by event-related fMRI of repetition priming.

We conducted two event-related functional magnetic resonance imaging (fMRI) experiments to investigate the neural substrates of visual object recognition in humans. We used a repetition-priming method with visual stimuli recurring at unpredictable intervals, either with the same appearance or with changes in size, viewpoint or exemplar. Lateral occipital and posterior inferior temporal cortex showed lower activity for repetitions of both real and non-sense objects; fusiform and left inferior frontal regions showed decreases for repetitions of only real objects. Repetition of different exemplars with the same name affected only the left inferior frontal cortex. Crucially, priming-induced decreases in activity of the right fusiform cortex depended on whether the three-dimensional objects were repeated with the same viewpoint, regardless of whether retinal image size changed; left fusiform decreases were independent of both viewpoint and size. These data show that dissociable subsystems in ventral visual cortex maintain distinct view-dependent and view-invariant object representations.

Adult↗

PubMed2002

Directing attention to locations and to sensory modalities: multiple levels of selective processing revealed with PET.

We used positron emission tomography (PET) to investigate the neural correlates of selective attention in humans. We examined the effects of attending to one side of space versus another (spatial selection) and to one sensory modality versus another (intermodal selection) during bilateral, bimodal stimulation of vision and touch. Attention toward one side resulted in greater activity in several contralateral areas. In somatosensory cortex, these spatial attentional modulations were found only when touch was relevant. In the intraparietal sulcus, spatial attentional effects were multimodal, independent of the modality attended. In occipital areas, spatial modulations were also found during both visual and tactile attention, indicating that tactile attention can affect activity in visual cortex; but occipital areas also showed more activity overall during visual attention. This suggests that while spatial attention can exert multimodal influences on visual areas, these still maintain their specificity for the visual modality. Additionally, irrespective of the attended side, attending to vision activated posterior parietal and superior premotor cortices, while attending to touch activated the parietal operculi. We conclude that attentional selection operates at multiple levels, with attention to locations and attention to modalities showing distinct effects. These jointly contribute to boost processing of stimuli at the attended location in the relevant modality.

Adult↗