Functional magnetic resonance imaging (fMRI) has become a ubiquitous tool in cognitive neuroscience. The technique allows the non-invasive measurements of cortical responses, but only on the millimeter scale. Recently, two methods aimed at studying the selectivity of neuronal populations on a subvoxel scale. The first technique, fMRI adaptation, relies on the observation that the fMRI response in a given voxel is reduced after prolonged presentation of a stimulus, and that this reduction is selective to the characteristics of the repeated stimuli. The second technique, multi-variate pattern analysis (MVPA), makes use of multi-variate statistics to recover small biases in individual voxels. This thesis compared the two techniques with the aim of studying early- and mid-level processing in the visual cortex. Chapter 3 investigated whether adaptation and MVPA provide consistent results about the properties of the cortical areas under study. To address this question, this thesis compared the two methods for their ability to detect the well documented orientation selectivity in early visual cortex. Using optimised experimental designs for each, this thesis found that the MVPA approach was more sensitive to small differences in stimulus orientation than the adaptation paradigm. Estimates of orientation selectivity obtained with the two methods were, however, very highly correlated across visual areas. Chapters 4 and 5 used both techniques to investigate how local orientation signals are combined and detected in intermediate levels of visual processing. In both chapters the MVPA was more efficient in detecting differences between stimulus categories. In particular, chapter 4 used plaid stimuli, made of the linear sum of two sinusoidal gratings. We obtained weak but consistent evidence, pointing to the direction that V2 might play a role in Fourier component integration. Chapter 5 used contour stimuli constructed from two luminance modulated sinusoidal gratings, with different orientations. Whereas, adaptation failed to reveal contour selectivity, MVPA accuracy was high in most areas tested. However, the experiment did not reveal a significant difference between the test and control conditions. Chapter 6 investigated the encoding of spatial phase in the cortex. Phase is a fundamental aspect of spatial vision, crucial both for the extraction of local features and overall scene perception. This thesis showed that several visual areas, including the primary visual cortex, were sensitive to relative phase combinations. However, phase coherence was optimally encoded in extrastriate areas as predicted by the physiological properties of higher regions.

This thesis concerns the investigation of metabolic changes in 1H metabolite levels in the human visual cortex due to visual stimulation using proton magnetic resonance spectroscopy (1H-MRS) at 7T. The work described in this thesis has been undertaken by the author and collaborators at the Sir Peter Mansfield Magnetic Resonance Centre at the University of Nottingham. Detection of functional changes in 1H metabolites may enable a greater understanding of neurotransmitter activity and metabolic pathways used for energy synthesis during activation of brain tissue. Previous 1H MRS studies of the activated human brain mainly focused on observing lactate (Lac) changes. More recent studies by Mangia et al, taking advantage of the increased signal and spectral resolution at 7T, have investigated the change in the level of Lac, glutamate (Glu), Aspartate (Asp) and Glucose (Glc) during activation. However, Mangia, did not measure significant change in the level of gamma aminobutyric acid (GABA) and Glutamine (Gln), which might be expected to change due to increased neurotransmitter cycling rates during activation. Given that the metabolite changes observed due to visual stimulation were relatively small. We used a long, intense visual stimulus, designed to retain attention, to confirm and quantify the changes in the levels of Glu, GABA, and Gln, and to further investigate the Lac and Asp response to visual stimulation. Our present results using a moving stimulus of full-screen flickering contrast-defined wedges, have demonstrated many more metabolic changes throughout two different time scales of stimulation. Small (2~11%) but significant stimulation induced increases in Lac, Glu and glutathione (GSH) were observed along with decreases in Asp, GIn and glycine (Gly). In addition, decreases in (intracellular) Glc and increases in GABA were seen but did not reach significance. The opposite changes in Glu and Asp are indicative of increased activity of the malate-aspartate shuttle, which taken together with the opposite changes in Glc and Lac reflect the expected increase in brain energy metabolism. The increases in Glu and GABA coupled with the decrease in GIn can be interpreted in terms of increased activity of the Glu/Gln and Gln/Glu/GABA neurotransmitter cycles. An entirely new observation is the increase of GSH during prolonged visual stimulation. The similarity of its time course to that of Glu suggests that it may be a response to the increased release of Glu or to the increased production of reactive oxygen species. Gly is also a precursor of GSH and a decrease on activation is consistent with increased GSH synthesis. Together these observations constitute the most detailed analysis to date of functional changes in human brain metabolites. Interestingly, the Lac response was confined to the first visual stimulus. It is possible that processes triggered during the first period of visual stimulation, could continue for a while after stimulation has ended. If this is an important mechanism of the activity-stimulated brain Lac response, shortening the duration of the first stimulus might lead to an increase in Lac response during the second period of stimulation. With this in mind, we designed a repeated visual stimulation paradigm, varying the duration of the first stimulation (shorter than 9.9-min, based on our previous results), to see the effect on the Lac response during the second visual stimulation period. A gradual increase in Lac under the prolonged stimulation, following the first brief stimulation (1s, 16s and 48s, respectively), was observed and maintained until the end of these periods. Lac responses during the second stimulation period looked similar whether the first stimulation was 1s or 16s. With the increase of first visual stimulus duration (48s), the Lac response under the second stimulation period was slightly diminished. No significant Lac accumulation can be evident to the second stimulation, when the initial stimulation was 288s. The averaged Lac level was considerably below baseline after cessation of the first 288s stimulus. It is possible that the increased glycolytic flux, triggered during the initial longer stimulation, would still continue for a while during recovery, accounting for the decreased brain Lac level during resting periods from stimulation. Further experiments are ongoing, varying the duration of the second resting periods, to see the effect on the Lac response to the second stimulation.

This thesis reports eight experiments which investigate voluntary emotional expressions in head-injured and normal children and four experiments which investigate spontaneous expressiveness in head-injured and normal children. A novel technique using dynamic video film was used to elicit more truly spontaneous expressions and then surreptitiously video the child's expressive responses to the film clips. In the voluntary condition children posed expressions on verbal request and imitated expressions depicted in photographs. Independent adult raters then viewed still images of the children's' expressions and categorised them for emotion shown and rated intensity of expression. Results indicated that for the spontaneous expressions not all film clips elicited expressions equally as well. The best clips were those that elicited happiness, sadness and disgust and differences in expressiveness were shown to exist between the head-injured and normal children. The acquired head-injury children as a group were significantly less expressive than the controls while differential effects on positive and negative spontaneous expression were found in left and right congenital hemiplegics. In right hemiplegics (left brain damage) the spontaneous expressions of disgust, sadness and happiness were poorer than controls, while in left hemiplegics (right brain damage) only negative spontaneous expressions of disgust and sadness were poorer than controls. These findings add new information to the existing body of knowledge in that they suggest that the left hemisphere is more important than one thought for the expression of negative emotion. The results from the voluntary production conditions indicated that the head-injured children could accurately imitate expressions suggesting that their ability to manipulate facial muscles was intact. However, the acquired head-injury children were found to be poorer than controls at producing expressions on verbal request particularly so in the left brain damage group.

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Recognition memory is a part of declarative memory; defined as the ability to discriminate previously presented stimuli from novel stimuli (Squire, Wixted & Clark, 2007). This thesis reports eight experiments that investigated factors that modulate recognition memory using a recognition memory paradigm that reflects the space learning effect (Greene, 1989) and repetition. Results from chapter two varied the space between stimuli repetition across two presentations and found that stimuli that is repeated following a short delay, and then repeated again following a longer delay led to poorer recognition memory compared to other variations. Additionally, results showed impaired recognition for older adults compared to younger adults for first repetition, but not for the second repetition, where no age effects were found (Experiment 1). Electroencephalography (EEG) technique (Experiment 2) examined the old/new effects (higher mean amplitude for old items compared to new items) pertaining to familiarity, recollection and post-retrieval monitoring through the three signatures commonly found in recognition memory, i.e. FN400, late positive component (LPC) and the late frontal effect (LFE) respectively to understand the underlying processes that supports repetition. Contrary to prior research, results showed an absence of the FN400 and LPC effect. However, with respect to the LFE, there was a reverse old/new effect in the left anterior superior (LAS) region for stimuli repeated for the first time which can be attributed to decision making, memory evaluation, and confidence in line with past literature (Allan et al, 1998; Ally & Budson, 2007; Ally et al. 2008; Dobbins & Han, 2006; Fleck, Daselaar, Dobbins & Cabeza, 2006). Chapter 3 investigated the effects of uni-modal (auditory or visual presented alone) and multi-modal stimuli, i.e. auditory and visual modality presented together (cross-modal), on recognition memory. The results show that unlike visual and cross-modal memory retrieval, repetition does not facilitate auditory recognition memory. The results also show that participants have higher d’ scores in the cross-modal stimuli compared to uni-modal stimuli (experiment 3). Although older participants show benefits with cross-modal stimuli, and with repetition, they still performed poorer compared to their younger counterparts (experiment 4). Chapter four investigated semantic congruency of multi-modal pairs in recognition memory. The results show that this effect only lasts for the first repetition and is absent for subsequent repetitions, for both older and younger adults (experiment 5). ERP results showed the presence of the FN400 old/new effect for trials repeated for the second time in the LAS region indicating recognition may be supported by familiarity for items repeated for the second time. In contraction to past research, there was no LPC or the LFE effects seen (experiment 6). Lastly, chapter five focuses on recognition memory in relation to modality mismatch. Modality mismatch is a situation that arises when information is encountered in a different modality compared to when it was initially presented (Mulligan & Osborn, 2009). The results from chapter five shows that auditory modality impairs recognition when it is either presented initially, or after a short delay. However, auditory presentations with a semantically associated pair (visual), either at initial presentation, or only if its pair was encountered after a short delay, there was no significant effect of modality mismatch at long delay (experiment 7). Results showed an absence of the FN400 effect indicating that FN400 effect is sensitive to perceptual match in line with Tsivilis et. al (2001). Lastly, experiment 8 showed that in the presence of modality mismatch, ERP results suggest that participants may rely on recollection to guide recognition process as seen by the presence of the LPC effect. Furthermore, the LPC also seems to index the amount of information to be retrieved consistent to past research (Fjell, Walhovd & Reinvang, 2005; Vilberg, Moosavi & Rugg, 2006), whereby larger amplitude were seen when the trial was in the cross-modal format compared to uni-modal format. As for the LFE component, the presence of the larger mean amplitude in the superior regions for uni-modal trials repeated for the second time suggests further post-retrieval monitoring associated with retrieval of additional information presented initially. Overall findings of this thesis have explored the factors that affect recognition memory, namely repetition, modality and age, and attempted to determine the underlying processes supporting recognition memory when items are repeated, or pairs of stimuli are semantically associated or modality is mismatched during encoding. This is particularly implicated in learning environments, providing further understanding in how repetition can enhance memory and its effects in environments where incongruent information is received, or repeated information encountered in a different modality.

Background: The brain is the most commonly affected organ during Toxoplasma gondii infection but the mechanisms utilized by this protozoan parasite for disrupting the brain's endothelial cells lining the blood–brain barrier (BBB) and moving to invade the brain are not yet understood. In the present study, we investigated the cellular pathogenicity of T. gondii infection in human brain microvascular endothelial cells (HBMECs), a fundamental component of the BBB. Methods: Intracellular development of T. gondii tachyzoites within HBMECs was characterized by using Acridine Orange (AO) staining. The integrity of HBMECs moolayer and tight junction permeability during T. gondii infection were assessed using transendothelial electrical resistance (TEER). Morphological changes associated with infection was assessed by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Cell viability and metabolic changes associated with infection were identified using alamar blue and nuclear magnetic resonance (1H NMR). The changes in lipid content and fatty acid composition of the total phospholipids were evaluated using LipidTox staining and gas chromatography (GC). The changes in the content of trace elements in response to T. gondii infection was assessed using inductively coupled plasma mass spectrometry (ICP-MS). Results and Discussion: The invasion, growth, and replication of T. gondii tachyzoites within HBMECs are possible, with disruption of the integrity and viability of the host cell through the course of infection. AO staining of T. gondii tachyzoites infecting HBMECs showed a marked increase in the surface area of tachyzoites during infection, indicating that tachyzoites invade their host cell and form their own compartments (PV) in which tachyzoites proliferate with a generation time of 24 h, eventually leading to cell rupture and exit of the parasites. A decrease was noted in the TEER of infected cells compared to uninfected controls, indicating that the invasion of the HBMECs by T. gondii had detectable effects on the integrity HBMECs monolayer by increased tight junction permeability. Morphological analysis revealed that the intracellular development of the tachyzoites disruption of tight junctions HBMECs monolayer and reorganization of some organelles of the host cell, such as the mitochondria, endoplasmic reticulum, and Golgi apparatus around the Parasitophorous vacuole membrane (PVM) and remained stable throughout the growth of the tachyzoites. The tight association between the PVM and host organelles may provide lipids and other macromolecules for parasite survival, proliferation, membrane biogenesis, and energy requirement. A marked decrease was noted in cell viability of infected cells at 48 h PI, compared to uninfected controls by alamar blue assay, indicating that growth of the parasites that cause a metabolic burden on the host cells. Metabolite analysis of HBMECs infected with T. gondii revealed a drastic increase in lactate and glutamine levels, as well as a reduction in choline and myo-inositol levels with infection. A drastic increase in lactate and glutamine levels may be attributed to the fact that T. gondii requires energy from the host, primarily via glycolysis and glutaminolysis. It is believed that increased lactate and glutamine levels result in increased paracellular permeability. A drastic reduction in choline and myo-inositol levels suggests the use of host lipid fractions for increased membrane maintenance or parasite lipid anabolism. It is believed that increased phosphatidylcholine levels result in altered monolayer permeability. Fatty acid analysis of HBMECs infected with T. gondii revealed a significant increase in C18:0 and C18:1n9c. It is believed that increased monounsaturated and polyunsaturated fatty acids result in increased tight junction permeability via modulated occludin and ZO-1 localization. Trace element analysis of HBMECs infected with T. gondii revealed a significant increase in Zn, Fe, Mg, and Cd levels, as well as a reduction in Co levels in growth medium obtained from the infected cells compared to non-infected controls. It is possible that altered trace elements levels, whether a parasite-induced or host-cell response, is important for protection against cellular oxidative stress and DNA damage during infection, and for suppressing cell apoptosis. In conclusion, the results obtained show that HBMECs permit the invasion, growth and proliferation of T. gondii tachyzoites and that infection can disrupt tight junction permeability and cause multiple morphological changes in the relocation of the host cell organelles around the PV and changes in the levels of host cell metabolites and trace elements. These findings provide a more in depth understanding of how T. gondii replicate within the HBMECs during infection, which may lead to novel ways to prevent or treat this disease.

The dorsal horn of the spinal cord is a complex laminar structure integrating exteroceptive signals from the primary afferent fibers into the central nervous system. The laminae of the spinal cord exhibit specialised roles and distinct processes occur across the axes of the dorsal horn. One of the most common in vivo approaches to recording spinal activity is single unit electrophysiology of cells that are believed to be representative of the subjects perception of stimuli. This approach has produced invaluable data but has not progressed in over half a century and fails to account for the specialised processes that occur in each lamina as well as the considerable cellular heterogeneity within and between laminae. In this thesis the use of linear multi-electrode array technology with 16 electrodes spaced 50 μm apart to have a total range of 750 μm that allows for simultaneous recordings across the laminae is developed and validated for the spinal dorsal horns of adult Sprague-Dawley rats. To do this a series of experiments were performed. The placement of the electrode was first optimised by creating a somatotopic map of evoked activity following hindpaw stimulation. A comprehensive series of electrical stimuli designed to induce differential primary afferent fiber activity were then given to establish how well the array could interpret fiber evoked activity. Mechanical and thermal stimulus paradigms were examined to evaluate the spatial distribution of responses across the dorsal horn; after optimisation the responses were then examined in the contexts of acute and chronic pain models. We found that the results of the unsorted multi-spike activity across the array correlated extremely well with predicted responses from single-unit studies in the existing literature. Fiber specific activation restricted along the dorso-ventral axis was detected as was the encoding of mechanical and thermal stimuli that were both innocuous and nocuous in nature. Comparisons between local field potentials and spike activity showed that multi-spike activity represented spinal processing of incoming signals significantly better. Induction of pain models strengthened the argument for the use of the technique by showing that it is capable of being used in both longitudinal and multi-treatment group studies. The approach produced vastly more data than the single-unit technique it builds upon with few drawbacks.

Past research tells us that individuals can infer information about a target’s emotional state and intentions from their facial expressions (Frith & Frith, 2012), a process known as mentalising. More recently, it has been found that this ability extends to inferring the events that caused the facial reaction (e.g. Pillai, Sheppard, & Mitchell, 2012; Pillai et al., 2014), an ability known as retrodictive mindreading. In the current thesis, we enter a new territory where a series of experiments was conducted to investigate whether people (perceivers) can guess a target’s social context by observing their response to emotional stimuli. The core findings were: 1) perceivers were able to discriminate whether the targets were alone or observed by another person, 2) without any knowledge of the social context or what the targets were watching, perceivers judged whether targets were hiding or exaggerating their facial expressions, and their judgments discriminated between conditions in which targets were observed and alone, and 3) perceivers’ eye movements also systematically discriminated between conditions in which targets were observed and alone. Perceivers were thus able to infer – explicitly or implicitly - a target’s social context by observing their emotional response. Therefore, the findings demonstrate that people have the ability to use other people’s minds as a window onto a social context that could not be seen directly.

Internal or Reflective attention can refer to our thoughts/reflections in order to make sense of our external world through our senses and perception. Reflective attention also includes the act of refreshing which is the act of thinking back and shifting internal attention towards previously activated mental representations. Previous research (M.R. Johnson et al., 2013) has shown that refreshing mirrors a striking similarity to that of inhibition of return (IOR) effect which inhibits visual attention to return to a previously cued location (Posner & Cohen, 1984; Posner, Rafal, Choate, & Vaughan, 1985). This IOR-like mechanism helps facilitate our thoughts (similarly to perception) by encouraging internal attention to move towards new information and avoid constant fixation on a single thought (M.R. Johnson et al., 2013) which was coined as reflective IOR (rIOR). The objective of the thesis investigates variables such as time duration and language during the production of rIOR mechanism. A total of seven experiments were conducted. The first set of experiments (Experiments 1 to 3) aimed to examine the time course of refreshing while the second set and (Experiments 4 to 7) examined the effect of language on reflective attention. In each experiment, participants were shown two stimuli, either in the form of pictures or English/Malay words. They were instructed to refresh by keeping one item (i.e., mental representation) active while ignoring the other. Results showed an attentional shift or bias towards the unrefreshed mental representation, more so in the experiments which used word stimuli rather than picture stimuli. The novelty of the current thesis is that early language processing (i.e., English and Malay words) in bilingual speakers was taken into account while investigating the reflective attention. This pattern was consistent whether the words were presented in English or Malay which are consistent with M. R. Johnson and colleagues’ finding that IOR mechanism shifts internal attention to new information However, if participants were presented with English stimuli, refreshed the English word but were then probed in the equivalent Malay word, a stronger priming effect emerged instead. The behavioural pattern implicated that asymmetrical cost during language switching could be reduced as a result of refreshing. The data also showed that while refreshing may cause a temporary inaccessibility to recently activated items, refreshed words were more memorable in a later recognition task. This suggested the role of refreshing plays an important role encoding and storing mental representations in later long term retrieval. Mental representations that were ignored or were not give n attention tended to fade away more quickly. The novelty of the thesis is that language processing was explored as a component to this mechanism by manipulating languages of the refreshed words presented. Participants were more likely to make false alarms when they were presented with an English equivalent word in the recognition task, when the original word had in fact been presented (i.e., previously refreshed) in Malay. Language models such as the Revised Hierarchical Model (RHM) ( Kroll and Stewart, 1990, 1994) were applied in examining refreshing in stronger or weaker languages that gave rise to poor memory performance. According to the RHM’s logic, words activated in non-dominant language would subsequently activate words in the dominant language in order to access the meaning of the word. In this language processing route, it is possible that refreshing a word in the weaker language would subsequently activate the similar word in the stronger language which is reflected as a false memory incident.