Oscillatory brain activity in memory disorders

Neuronal oscillations are thought to underlie interactions between distinct brain regions required for normal memory functioning. This study aimed at elucidating the neuronal basis of memory abnormalities in neurodegenerative disorders. Magnetoencephalography (MEG) was used to measure oscillatory brain signals in patients with Alzheimer s disease (AD), a neurodegenerative disease causing progressive cognitive decline, and mild cognitive impairment (MCI), a disorder characterized by mild but clinically significant complaints of memory loss without apparent impairment in other cognitive domains. Furthermore, to help interpret our AD/MCI results and to develop more powerful oscillatory MEG paradigms for clinical memory studies, oscillatory neuronal activity underlying declarative memory, the function which is afflicted first in both AD and MCI, was investigated in a group of healthy subjects. An increased temporal-lobe contribution coinciding with parieto-occipital deficits in oscillatory activity was observed in AD patients: sources in the 6 12.5 Hz range were significantly stronger in the parieto-occipital and significantly weaker in the right temporal region in AD patients, as compared to MCI patients and healthy elderly subjects. Further, the auditory steady-state response, thought to represent both evoked and induced activity, was enhanced in AD patients, as compared to controls, possibly reflecting decreased inhibition in auditory processing and deficits in adaptation to repetitive stimulation with low relevance. Finally, the methodological study revealed that successful declarative encoding and retrieval is associated with increases in occipital gamma and right hemisphere theta power in healthy unmedicated subjects. This result suggests that investigation of neuronal oscillations during cognitive performance could potentially be used to investigate declarative memory deficits in AD patients. Taken together, the present results provide an insight on the role of brain oscillatory activity in memory function and memory disorders.

Music in the recovering brain

Listening to music involves a widely distributed bilateral network of brain regions that controls many auditory perceptual, cognitive, emotional, and motor functions. Exposure to music can also temporarily improve mood, reduce stress, and enhance cognitive performance as well as promote neural plasticity. However, very little is currently known about the relationship between music perception and auditory and cognitive processes or about the potential therapeutic effects of listening to music after neural damage. This thesis explores the interplay of auditory, cognitive, and emotional factors related to music processing after a middle cerebral artery (MCA) stroke. In the acute recovery phase, 60 MCA stroke patients were randomly assigned to a music listening group, an audio book listening group, or a control group. All patients underwent neuropsychological assessments, magnetoencephalography (MEG) measurements, and magnetic resonance imaging (MRI) scans repeatedly during a six-month post-stroke period. The results revealed that amusia, a deficit of music perception, is a common and persistent deficit after a stroke, especially if the stroke affects the frontal and temporal brain areas in the right hemisphere. Amusia is clearly associated with deficits in both auditory encoding, as indicated by the magnetic mismatch negativity (MMNm) response, and domain-general cognitive processes, such as attention, working memory, and executive functions. Furthermore, both music and audio book listening increased the MMNm, whereas only music listening improved the recovery of verbal memory and focused attention as well as prevented a depressed and confused mood during the first post-stroke months. These findings indicate a close link between musical, auditory, and cognitive processes in the brain. Importantly, they also encourage the use of listening to music as a rehabilitative leisure activity after a stroke and suggest that the auditory environment can induce long-term plastic changes in the recovering brain.

Cortical processing of speech and non-speech sounds in adults and newborns

Comprehension of a complex acoustic signal - speech - is vital for human communication, with numerous brain processes required to convert the acoustics into an intelligible message. In four studies in the present thesis, cortical correlates for different stages of speech processing in a mature linguistic system of adults were investigated. In two further studies, developmental aspects of cortical specialisation and its plasticity in adults were examined. In the present studies, electroencephalographic (EEG) and magnetoencephalographic (MEG) recordings of the mismatch negativity (MMN) response elicited by changes in repetitive unattended auditory events and the phonological mismatch negativity (PMN) response elicited by unexpected speech sounds in attended speech inputs served as the main indicators of cortical processes. Changes in speech sounds elicited the MMNm, the magnetic equivalent of the electric MMN, that differed in generator loci and strength from those elicited by comparable changes in non-speech sounds, suggesting intra- and interhemispheric specialisation in the processing of speech and non-speech sounds at an early automatic processing level. This neuronal specialisation for the mother tongue was also reflected in the more efficient formation of stimulus representations in auditory sensory memory for typical native-language speech sounds compared with those formed for unfamiliar, non-prototype speech sounds and simple tones. Further, adding a speech or non-speech sound context to syllable changes was found to modulate the MMNm strength differently in the left and right hemispheres. Following the acoustic-phonetic processing of speech input, phonological effort related to the selection of possible lexical (word) candidates was linked with distinct left-hemisphere neuronal populations. In summary, the results suggest functional specialisation in the neuronal substrates underlying different levels of speech processing. Subsequently, plasticity of the brain's mature linguistic system was investigated in adults, in whom representations for an aurally-mediated communication system, Morse code, were found to develop within the same hemisphere where representations for the native-language speech sounds were already located. Finally, recording and localization of the MMNm response to changes in speech sounds was successfully accomplished in newborn infants, encouraging future MEG investigations on, for example, the state of neuronal specialisation at birth.

Towards a Critique of the Concept of the Right to Self-Determination in Africa : A Conceptual Examination and the Cases of Western Sahara, Southern Sudan and Eritrea

This thesis examines the right to self-determination which is a norm used for numerous purposes by multiple actors in the field of international relations, with relatively little clarity or agreement on the actual and potential meaning of the right. In international practice, however, the main focus in applying the right has been in the context of decolonization as set by the United Nations in its early decades. Thus, in Africa the right to self-determination has traditionally implied that the colonial territories, and particularly the populations within these territories, were to constitute the people who were entitled to the right. That is, self-determination by decolonization provided a framework for the construction of independent nation-states in Africa whilst other dimensions of the right remained largely or totally neglected. With the objective of assessing the scope, content, developments and interpretations of the right to self-determination in Africa, particularly with regard to the relevance of the right today, the thesis proceeds on two fundamental hypotheses. The first is that Mervyn Frost s theory of settled norms, among which he lists the right to self-determination, assumes too much. Even if the right to self-determination is a human right belonging to all peoples stipulated, inter alia, in the first Article of the 1966 International Human Rights Covenants, it is a highly politicized and context-bound right instead of being settled and observed in a way that its denial would need special justification. Still, the suggested inconsistency or non-compliance with the norm of self-determination is not intended to prove the uselessness or inappropriateness of the norm, but, on the contrary, to invite and encourage debate on the potential use and coverage of the right to self-determination. The second hypothesis is that within the concept of self-determination there are two normative dimensions. One is to do with the idea and practice of statehood, the nation and collectivity that may decide to conduct itself as an independent state. The other one is to do with self-determination as a human right, as a normative condition, to be enjoyed by people and peoples within states that supersedes state authority. These external and internal dimensions need to be seen as complementary and co-terminous, not as mutually exclusive alternatives. The thesis proceeds on the assumption that the internal dimension of the right, with human rights and democracy at its core, has not been considered as important as the external. In turn, this unbalanced and selective interpretation has managed to put the true normative purpose of the right making the world better and bringing more just polity models into a somewhat peculiar light. The right to self-determination in the African context is assessed through case studies of Western Sahara, Southern Sudan and Eritrea. The study asks what these cases say about the right to self-determination in Africa and what their lessons learnt could contribute to the understanding and relevance of the right in today s Africa. The study demonstrates that even in the context of decolonization, the application of the right to self-determination has been far from the consistent approach supposedly followed by the international community: in many respects similar colonial histories have easily led to rather different destinies. While Eritrea secured internationally recognized right to self-determination in the form of retroactive independence in 1993, international recognition of distinct Western Sahara and Southern Sudan entities is contingent on complex and problematic conditions being satisfied. Overall, it is a considerable challenge for international legality to meet empirical political reality in a meaningful way, so that the universal values attached to the norm of self-determination are not overlooked or compromised but rather reinforced in the process of implementing the right. Consequently, this thesis seeks a more comprehensive understanding of the right to self-determination with particular reference to post-colonial Africa and with an emphasis on the internal, human rights and democracy dimensions of the norm. It is considered that the right to self-determination cannot be perceived only as an inter-state issue as it is also very much an intra-state issue, including the possibility of different sub-state arrangements exercised under the right, for example, in the form of autonomy. At the same time, the option of independent statehood achieved through secession remains a mode of exercising and part of the right to self-determination. But in whatever form or way applied, the right to self-determination, as a normative instrument, should constitute and work as a norm that comprehensively brings more added value in terms of the objectives of human rights and democracy. From a normative perspective, a peoples right should not be allowed to transform and convert itself into a right of states. Finally, in light of the case studies of Western Sahara, Southern Sudan and Eritrea, the thesis suggests that our understanding of the right to self-determination should now reach beyond the post-colonial context in Africa. It appears that both the questions and answers to the most pertinent issues of self-determination in the cases studied must be increasingly sought within the postcolonial African state rather than solely in colonial history. In this vein, the right to self-determination can be seen not only as a tool for creating states but also as a way to transform the state itself from within. Any such genuinely post-colonial approach may imply a judicious reconsideration, adaptation or up-dating of the right and our understanding of it in order to render it meaningful in Africa today.