R. Martyn Bracewell

Are faces special? A case of pure prosopagnosia

The ability to recognize individual faces is of crucial social importance for humans and evolutionarily necessary for survival. Consequently, faces may be “special” stimuli, for which we have developed unique modular perceptual and recognition processes. Some of the strongest evidence for face processing being modular comes from cases of prosopagnosia, where patients are unable to recognize faces whilst retaining the ability to recognize other objects. Here we present the case of an acquired prosopagnosic whose poor recognition was linked to a perceptual impairment in face processing. Despite this, she had intact object recognition, even at a subordinate level. She also showed a normal ability to learn and to generalize learning of nonfacial exemplars differing in the nature and arrangement of their parts, along with impaired learning and generalization of facial exemplars. The case provides evidence for modular perceptual processes for faces.

Challenges of proper placebo control for non-invasive brain stimulation in clinical and experimental applications

A range of techniques are now available for modulating the activity of the brain in healthy people and people with neurological conditions. These techniques, including transcranial magnetic stimulation (TMS) and transcranial current stimulation (tCS, which includes direct and alternating current), create magnetic or electrical fields that cross the intact skull and affect neural processing in brain areas near to the scalp location where the stimulation is delivered. TMS and tCS have proved to be valuable tools in behavioural neuroscience laboratories, where causal involvement of specific brain areas in specific tasks can be shown. In clinical neuroscience, the techniques offer the promise of correcting abnormal activity, such as when a stroke leaves a brain area underactive. As the use of brain stimulation becomes more commonplace in laboratories and clinics, we discuss the safety and ethical issues inherent in using the techniques with human participants, and we suggest how to balance scientific integrity with the safety of the participant.

Brain stimulation studies of non-motor cerebellar function: A systematic review

Evidence for a cerebellar role in non-motor functions has been demonstrated by clinical and neuroimaging research. These approaches do not allow causal relationships to be inferred though the experimental manipulation of the cerebellum. Transcranial magnetic and current stimulation may allow better understanding of the cerebellum via the temporary alteration of its operation in healthy volunteers. This review examined all studies of the cerebellar role in non-motor functions using non-invasive brain stimulation. Of 7585 papers captured by an initial search, 26 met specific selection criteria. Analysis revealed behavioural effects across learning, memory, cognition, emotional processing, perception and timing, though the results were not sufficiently similar as to offer a definitive statement of the cerebellums role. The non-invasive application of stimulation to the cerebellum presents challenges due to surrounding anatomy and the relatively small target areas involved. This review analysed the methods used to address these challenges with a view to suggesting methodological improvements for the establishment of standards for the location of cerebellar stimulation targets and appropriate levels of stimulation.

Feature integration in visual working memory: parietal gamma activity is related to cognitive coordination.

The mechanism by which distinct subprocesses in the brain are coordinated is a central conundrum of systems neuroscience. The parietal lobe is thought to play a key role in visual feature integration, and oscillatory activity in the gamma frequency range has been associated with perception of coherent objects and other tasks requiring neural coordination. Here, we examined the neural correlates of integrating mental representations in working memory and hypothesized that parietal gamma activity would be related to the success of cognitive coordination. Working memory is a classic example of a cognitive operation that requires the coordinated processing of different types of information and the contribution of multiple cognitive domains. Using magnetoencephalography (MEG), we report parietal activity in the high gamma (80–100 Hz) range during manipulation of visual and spatial information (colors and angles) in working memory. This parietal gamma activity was significantly higher during manipulation of visual-spatial conjunctions compared with single features. Furthermore, gamma activity correlated with successful performance during the conjunction task but not during the component tasks. Cortical gamma activity in parietal cortex may therefore play a role in cognitive coordination.

Hand Interactions in Rapid Grip Force Adjustments Are Independent of Object Dynamics

Object manipulation requires rapid increase in grip force to prevent slippage when the load force of the object suddenly increases. Previous experiments have shown that grip force reactions interact between the hands when holding a single object. Here we test whether this interaction is modulated by the object dynamics experienced before the perturbation of the load force. We hypothesized that coupling of grip forces should be stronger when holding a single object than when holding separate objects. We measured the grip force reactions elicited by unpredictable load perturbations when participants were instructed to hold one single or two separate objects. We simulated these objects both visually and dynamically using a virtual environment consisting of two robotic devices and a calibrated stereo display. In contrast to previous studies, the load forces arising from a single object could be uncoupled at the moment of perturbation, allowing for a pure measurement of grip force coupling. Participants increased grip forces rapidly (onset approximately 70 ms) in response to perturbations. Grip force increases were stronger when the load force on the other hand also increased. No such coupling was present in the reaction of the arms to the load force increase. Surprisingly, however, the grip force interaction did not depend on the nature of the manipulated object. These results show fast obligatory coupling of bimanual grip force responses. Although this coupling may play a functional role for providing stability in bimanual object manipulation, it seems to constitute a relatively hard-wired modulation of a reflex.

Does transcranial direct current stimulation to prefrontal cortex affect mood and emotional memory retrieval in healthy individuals

Studies using transcranial direct current stimulation (tDCS) of prefrontal cortex to improve symptoms of depression have had mixed results. We examined whether using tDCS to change the balance of activity between left and right dorsolateral prefrontal cortex (DLPFC) can alter mood and memory retrieval of emotional material in healthy volunteers. Participants memorised emotional images, then tDCS was applied bilaterally to DLPFC while they performed a stimulus-response compatibility task. Participants were then presented with a set of images for memory retrieval. Questionnaires to examine mood and motivational state were administered at the beginning and end of each session. Exploratory data analyses showed that the polarity of tDCS to DLPFC influenced performance on a stimulus-response compatibility task and this effect was dependent on participants’ prior motivational state. However, tDCS polarity had no effect on the speed or accuracy of memory retrieval of emotional images and did not influence positive or negative affect. These findings suggest that the balance of activity between left and right DLPFC does not play a critical role in the mood state of healthy individuals. We suggest that the efficacy of prefrontal tDCS depends on the initial activation state of neurons and future work should take this into account.

Visuospatial transformation impairments in Parkinson's disease

Some previous studies have reported impairments in Parkinsons disease (PD) that affect performance on visuospatial tasks. The aim of this study was to further elucidate the underlying cognitive impairment to visuospatial processing in PD. Nondementing PD patients and neurologically normal, age-matched controls completed two tasks of visuospatial transformation. In Task 1, observers made perceptual matching judgments about the shape equivalence of two upright or rotated 2D novel patterns. Task 2 used a recognition memory paradigm in which participants first memorized a target object at a specific orientation and then made target/nontarget judgments to targets or visually similar distractors at varying orientations. Analyses of the regression slopes between response times and angular disparity showed that PD is associated with impairments affecting spatial transformation during image normalization in both tasks. The results also showed that the patients were more impaired, relative to controls, at spatial transformation during the perceptual matching of two images, than in the recognition memory task. It is suggested that PD can result in deficits affecting spatial transformation processes that are modulated by working memory and task demands.

Facilitation of Fast Backward Priming After Left Cerebellar Continuous Theta-Burst Stimulation

Traditional theories of backward priming account only for the priming effects found at long stimulus onset asynchronies (SOAs). Here, we suggest that the presence of backward priming at short SOAs may be related to the integrative role of the cerebellum. Previous research has shown that the right cerebellum is involved in forward associative priming. Functional magnetic resonance imaging reveals some activation of the left cerebellar hemisphere during backward priming; but what this activation represents is unclear. Here we explore this issue using continuous theta-burst transcranial magnetic stimulation (cTBS) and associative priming in a lexical decision task. We tested the hypothesis that the left cerebellum plays a role in backward priming and that this is dissociated from the role of the right cerebellum in forward priming. Before and after cTBS was applied to their left and right cerebellar hemispheres, participants completed a lexical decision task. Although we did not replicate the forward priming effect reported in the literature, we did find a significant increase in backward priming after left relative to right cerebellar cTBS. We consider how theories of cerebellar function in the motor domain can be extended to language and cognitive models of backward priming.

Chapter 14 – The Use of Transcranial Magnetic Brain Stimulation to Study Cerebellar Language Function

Abstract Many researchers now use noninvasive brain stimulation to investigate a wide range of problems in cognitive neuroscience. Transcranial magnetic stimulation (TMS) has been used successfully for more than a decade to study the functions of the cerebral cortex. There is now growing interest in applying TMS to the study of cerebellar functions. We briefly review studies that have used this technique to investigate linguistic functions of the cerebellum. Despite the relative ease of application of TMS to the region over the posterior fossa, several theoretical and methodological issues need to be carefully considered by workers in the field, whereas experimental results to date leave many questions unanswered. In particular, downstream effects of cerebellar stimulation on the cerebral cortex require to be rigorously evaluated. It is likely that TMS used in conjunction with electrophysiological recording will prove productive in future research.

What is the JRCPE for

The success of the Journal of the Royal College of Physicians of Edinburgh (JRCPE) depends in large part on receiving high quality, well-written articles, editorials and case reports. Writing for medical or scientific journals is not a skill with which most of us are born, but like all skills it can be learnt. This short article gives some general advice on how to write papers and case reports for the JRCPE, and also some advice on what the Editorial Board look for in an article or case report.