title: Numerical modelling of plasticity induced by transcranial magnetic stimulation

authors: Wilson, Marcus T.

subjects: Transcranial Magnetic Stimulation

abstract: We use neural field theory and spike-timing dependent plasticity to make a simple but biophysically reasonable model of long-term plasticity changes in the cortex due to transcranial magnetic stimulation (TMS). We show how common TMS protocols can be captured and studied within existing neural field theory. Specifically, we look at repetitive TMS protocols such as theta burst stimulation and paired-pulse protocols. Continuous repetitive protocols result mostly in depression, but intermittent repetitive protocols in potentiation. A paired pulse protocol results in depression at short (<∼10 ms) and long (>∼ 100 ms) interstimulus intervals, but potentiation for mid-range intervals. The model is sensitive to the choice of neural populations that are driven by the TMS pulses, and to the parameters that describe plasticity, which may aid interpretation of the high variability in existing experimental results. Driving excitatory populations results in greater plasticity changes than driving inhibitory populations. Modelling also shows the merit in optimizing a TMS protocol based on an individual’s electroencephalogram. Moreover, the model can be used to make predictions about protocols that may lead to improvements in repetitive TMS outcomes.

text: Numerical modelling of plasticity induced by transcranial magnetic stimulation We use neural field theory and spike-timing dependent plasticity to make a simple but biophysically reasonable model of long-term plasticity changes in the cortex due to transcranial magnetic stimulation (TMS). We show how common TMS protocols can be captured and studied within existing neural field theory. Specifically, we look at repetitive TMS protocols such as theta burst stimulation and paired-pulse protocols. Continuous repetitive protocols result mostly in depression, but intermittent repetitive protocols in potentiation. A paired pulse protocol results in depression at short (<∼10 ms) and long (>∼ 100 ms) interstimulus intervals, but potentiation for mid-range intervals. The model is sensitive to the choice of neural populations that are driven by the TMS pulses, and to the parameters that describe plasticity, which may aid interpretation of the high variability in existing experimental results. Driving excitatory populations results in greater plasticity changes than driving inhibitory populations. Modelling also shows the merit in optimizing a TMS protocol based on an individual’s electroencephalogram. Moreover, the model can be used to make predictions about protocols that may lead to improvements in repetitive TMS outcomes.

year: 2013

title: Distal occurrence of mid-Holocene Whakatane Tephra on the Chatham Islands, New Zealand, and potential for cryptotephra studies

authors: Holt, Katherine A.

subjects: New Zealand

abstract: The Whakatane Tephra, a rhyolitic tephra erupted ca. 5500 cal. BP from Okataina Volcanic Centre, central North Island, has been identified on the Chatham Islands which lie ˜900 km east of Christchurch, New Zealand. The visible tephra layer, ˜5 mm in thickness and preserved within peat on Pitt Island, was identified using both radiocarbon dating and analysis of glass shards by electron microprobe. Whakatane Tephra is the first Holocene tephra to be identified on the Chatham Islands, and it is the most distal Holocene tephra yet recorded in the New Zealand region, being ˜850 km from source. The Pitt Island occurrence extends the tephra's dispersal area markedly, by an order of magnitude, possibly to ˜300,000 km2. An estimated dispersal index (D) of approximately 105 km2 indicates that the eruption generated a very high plinian column, possibly exceeding ˜30 km in height, with strong winds blowing the ash plume southeastwards. This new discovery of distal Whakatane Tephra as a thin but visible layer strongly implies that cryptotephras are likely to be preserved on the Chatham Islands and within adjacent ocean floor sediments. Therefore the potential exists to develop enhanced cryptotephrostratigraphic records from these distal areas, which in turn would help facilitate precise correlation via tephrochronology of palaeoenvironmental records (such as NZ-INTIMATE) from mainland New Zealand, the southwest Pacific Ocean, and the Chatham Islands.

text: Distal occurrence of mid-Holocene Whakatane Tephra on the Chatham Islands, New Zealand, and potential for cryptotephra studies The Whakatane Tephra, a rhyolitic tephra erupted ca. 5500 cal. BP from Okataina Volcanic Centre, central North Island, has been identified on the Chatham Islands which lie ˜900 km east of Christchurch, New Zealand. The visible tephra layer, ˜5 mm in thickness and preserved within peat on Pitt Island, was identified using both radiocarbon dating and analysis of glass shards by electron microprobe. Whakatane Tephra is the first Holocene tephra to be identified on the Chatham Islands, and it is the most distal Holocene tephra yet recorded in the New Zealand region, being ˜850 km from source. The Pitt Island occurrence extends the tephra's dispersal area markedly, by an order of magnitude, possibly to ˜300,000 km2. An estimated dispersal index (D) of approximately 105 km2 indicates that the eruption generated a very high plinian column, possibly exceeding ˜30 km in height, with strong winds blowing the ash plume southeastwards. This new discovery of distal Whakatane Tephra as a thin but visible layer strongly implies that cryptotephras are likely to be preserved on the Chatham Islands and within adjacent ocean floor sediments. Therefore the potential exists to develop enhanced cryptotephrostratigraphic records from these distal areas, which in turn would help facilitate precise correlation via tephrochronology of palaeoenvironmental records (such as NZ-INTIMATE) from mainland New Zealand, the southwest Pacific Ocean, and the Chatham Islands.

year: 2011

title: Replacing medical and social models of disability by a communities-based model of equal access for people of differing abilities: A Māori perspective

authors: Hickey, Huhana

subjects: New Zealand

abstract: I argue here that although the social model of disability which currently prevails in New Zealand is preferable in many ways to the earlier medical model, it is nevertheless based on a largely uni-dimensional concept of society and continues an established tradition of negativity, one that is evident in the ongoing use of the word 'disabled' itself by those who subscribe to the social model. I argue here that the social model of disability should be replaced by a communities-based model of equal access for people of differing abilities, one that is, in the New Zealand context, informed by a further developed Māori model of health and wellbeing proposed by Mason Durie, Te Whare Tapa Whā. This mode is designed in such a way as to accommodate difference and diversity. In the discussion of different models, I use the words 'disabled' and 'disability'; in other contexts, I replace 'disabled people' by 'people of differing abilities'.

text: Replacing medical and social models of disability by a communities-based model of equal access for people of differing abilities: A Māori perspective I argue here that although the social model of disability which currently prevails in New Zealand is preferable in many ways to the earlier medical model, it is nevertheless based on a largely uni-dimensional concept of society and continues an established tradition of negativity, one that is evident in the ongoing use of the word 'disabled' itself by those who subscribe to the social model. I argue here that the social model of disability should be replaced by a communities-based model of equal access for people of differing abilities, one that is, in the New Zealand context, informed by a further developed Māori model of health and wellbeing proposed by Mason Durie, Te Whare Tapa Whā. This mode is designed in such a way as to accommodate difference and diversity. In the discussion of different models, I use the words 'disabled' and 'disability'; in other contexts, I replace 'disabled people' by 'people of differing abilities'.

year: 2006-02