fMRI study of cutaneous illusions

We conducted three block-design experiments using functional magnetic resonance imaging (fMRI) to investigate the cortical areas involved in: 1) processing passively presented pneumatic stimulation, 2) the perception of tactile apparent motion (TAM), and 3) the perception of the cutaneous “rabbit.” In the first experiment (Arm Localizer), periods of random pneumatic stimulation delivered to the ventral right forearm were alternated with periods of rest. The results were consistent with previous research showing activation in the contralateral precentral and postcentral gyri, as well as higher parietal cortical areas. In the second experiment (Apparent Motion), periods of consecutive air puffs presented along the length of the forearm (apparent motion trials) were alternated with periods of random stimulation. The timing of the apparent motion trails was such that participants perceived a broad, continuous, unbroken sweep down the arm. Activation was observed in areas of the limbic occipital, and parietal lobes that are concerned with imagery. In the third experiment (Cutaneous “Rabbit”), periods in which five air puffs were delivered to a location proximal to the elbow, followed by five air puffs to a location proximal to the wrist (cutaneous “rabbit” trials), were alternated with periods of simultaneous air puffs to the same locations. The timing of the cutaneous “rabbit” trials was such that participants perceived a discretely localized train of air puffs between the two actual points of stimulation. Activation was observed primarily in areas of the parietal cortex concerned with tactile attention and the processing of somatosensory information. While it has been known for some time that TAM and the cutaneous “rabbit” are behaviourally distinct, the present study provides the first neuroimaging evidence that TAM and the cutaneous “rabbit” are represented in different areas of the human brain

The Tactile Motion Aftereffect

The tactile motion aftereffect (tMAE) is a perceptual phenomenon in which illusory motion is reported following adaptation to a unidirectionally moving tactile stimulus. Unlike its visual counterpart, relatively little is known about the tMAE. For that reason, the purpose of this dissertation was to gain a better understanding of the tMAE using both psychophysical and neuroimaging techniques. In a series of five experiments the skin was adapted using a plastic cylinder with a square-wave patterned surface. Chapter 2 consists of two experiments, both of which adapted the glabrous surface of the right hand. Experiment 1 showed that the prevalence, duration, and vividness of the tMAE did not differ between the fingers (thumb excluded), palm and fingers (thumb included), and palm and fingers (thumb excluded). Thus, the divergent prevalence rates of two previous studies (Hollins & Favorov, 1994; Lerner & Craig, 1994) cannot be explained by the inclusion of the thumb in the latter study. Experiment 2 showed that as adapting speed increased from 15 to 75 rpm so did the prevalence, duration, and vividness of the tMAE. Previously it has been shown that the tMAE duration increases with adapting duration (Hollins & Favorov, 1994). Given that speed * duration = distance, increasing either adapting speed or duration also increases distance. As such, it was unclear which parameter(s) caused the observed increase in prevalence, duration, and vividness. Chapter 3 manipulated adapting duration (1, 2, and 4 min) and speed (30 and 60 rpm) in the same experiment, thereby allowing the effect of distance to be assessed in the interaction. The results showed that the prevalence, duration, and vividness of the tMAE increased with adapting speed. There was also a positive relationship between adapting duration and prevalence, but not duration or vividness, of the illusion. Distance was only a factor when it came to the tMAE duration. To gain insight into the peripheral neural basis of the tMAE, Chapter 4 measured the prevalence, duration, and vividness of the tMAE on skin areas that differ in their composition of fast adapting (FA) mechanoreceptive units, namely the right cheek, volar surface of the forearm, and glabrous surface of the hand. While there was no difference in duration or vividness between the skin surfaces tested, the tMAE was reported twice as often on the hand than the cheek and forearm, which did not differ significantly from one another. This finding suggests that the tMAE can be induced by adapting FA type I (FA I) units in the glabrous skin (hand) and the hair follicle units (cheek and forearm) and/or the FA I (cheek) and field (forearm) units in the hairy skin. Chapter 5 investigated the central neural basis of the tMAE using functional magnetic resonance imaging (fMRI). Of the areas shown to be responsive to tactile motion on the glabrous surface of the right hand, namely the contralateral (left) thalamus, postcentral gyrus (PCG), and parietal operculum, only the PCG showed evidence of the tMAE; that is, there was a sustained fMRI response following the offset of the illusion trials (cylinder rotating at 60 rpm), but not the control trials (cylinder rotating at 15 rpm), presumably reflecting illusory motion perception. Taken together, the experiments described herein expand our knowledge of the tMAE. Using a cylinder adapting apparatus, it was shown that: prevalence is the best measure of tMAE strength; the tMAE is not as robust as its visual counterpart; adapting duration and speed positively affect the prevalence of the tMAE; the tMAE is twice as prevalent on the glabrous than the hairy skin; the FAI and hair follicle units likely underlie the tMAE; the tMAE is likely caused by adapting direction selective neurons in the contralateral PCG

Limbic grey matter changes in early Parkinson's disease

The purpose of this study was to investigate local and network related changes of limbic grey matter in early Parkinson’s disease (PD) and their interrelation with non-motor symptom severity. We applied voxel-based morphometric methods in 538 T1 MRI images retrieved from the Parkinson's Progression Markers Initiative website. Grey matter densities and cross-sectional estimates of age-related grey matter change were compared between subjects with early PD (n=366) and age-matched healthy controls (n=172) within a regression model, and associations of grey matter density with symptoms were investigated. Structural brain networks were obtained using covariance analysis seeded in regions showing grey matter abnormalities in PD subject group. Patients displayed focally reduced grey matter density in the right amygdala, which was present from the earliest stages of the disease without further advance in mild-moderate disease stages. Right amygdala grey matter density showed negative correlation with autonomic dysfunction and positive with cognitive performance in patients, but no significant interrelations were found with anxiety scores. Patients with PD also demonstrated right amygdala structural disconnection with less structural connectivity of the right amygdala with the cerebellum and thalamus but increased covariance with bilateral temporal cortices compared with controls. Age-related grey matter change was also increased in PD preferentially in the limbic system. In conclusion, detailed brain morphometry in a large group of early PD highlights predominant limbic grey matter deficits with stronger age-associations compared with controls and associated altered structural connectivity pattern. This provides in vivo evidence for early limbic grey matter pathology and structural network changes that may reflect extranigral disease spread in PD

Visual area V5/hMT+ contributes to perception of tactile motion direction: a TMS study

Human imaging studies have reported activations associated with tactile motion perception in visual motion area V5/hMT+, primary somatosensory cortex (SI) and posterior parietal cortex (PPC; Brodmann areas 7/40). However, such studies cannot establish whether these areas are causally involved in tactile motion perception. We delivered double-pulse transcranial magnetic stimulation (TMS) while moving a single tactile point across the fingertip, and used signal detection theory to quantify perceptual sensitivity to motion direction. TMS over both SI and V5/hMT+, but not the PPC site, significantly reduced tactile direction discrimination. Our results show that V5/hMT+ plays a causal role in tactile direction processing, and strengthen the case for V5/hMT+ serving multimodal motion perception. Further, our findings are consistent with a serial model of cortical tactile processing, in which higher-order perceptual processing depends upon information received from SI. By contrast, our results do not provide clear evidence that the PPC site we targeted (Brodmann areas 7/40) contributes to tactile direction perception

Sorcery beliefs and oral tradition in Cheticamp, Cape Breton

During the late nineteenth and early twentieth centuries in the Cheticamp area of Cape Breton, Nova Scotia, events took place which were considered to be the machinations of certain persons who were known to be sorciers. The people of Cheticamp reacted to these happenings by performing rituals which were believed to deliver the victim from the sorcery. Although sorcery is no longer practised in the community of Cheticamp, the tradition of belief in such practices lives on in contemporary oral tradition. -- An analysis of primary and secondary historical accounts in conjunction with such oral traditions of Cheticamp reveals narratives concerning sorcery, and esoteric and exoteric views and values of the community. These in turn suggest reasons for the activation of the sorcery beliefs during the period under consideration, and indicate the present state of these beliefs. -- The period from the 1870's to the 1930's witnessed changes in the traditional livelihood, family religion, and language of Cheticamp. This thesis hypothesizes that anxiety generated over these changes which threatened the values of the community, caused a belief in "sorcerie" to function as a means of social control