Lari Koponen

Lari Koponen
University of Birmingham · School of Psychology

PhD

About

47
Publications
5,970
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
453
Citations
Citations since 2016
42 Research Items
446 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
Introduction
Lari Koponen currently works at the Department of Psychiatry at Duke University. Lari's main ambition is to develop next generation of transcranial magnetic stimulation (TMS) technology and instrumentation. His previous project at Aalto University was to develop the first multi-locus TMS (mTMS) device. In addition to developing instrumentation, Lari has studied the human brain with TMS. Lari has is a long-term programming enthusiast with both low-level languages—such as C, C++, and CUDA—and high-level languages—such as Mathematica, Matlab and Python. Lari has written code to run on small embedded systems, FPGAs, and parallel processing on a cluster computer (with vectorized AVX2 code to extract the last bits of performance).

Publications

Publications (47)
Article
Full-text available
Transcranial magnetic stimulation (TMS) is widely applied on humans for research and clinical purposes. TMS studies on small animals, e.g., rodents, can provide valuable knowledge of the underlying neurophysiological mechanisms. Administering TMS on small animals is, however, prone to technical difficulties, mainly due to their small head size. In...
Article
Magnetoencephalography (MEG) based on optically pumped magnetometers (OPMs) has been hailed as the future of electrophysiological recordings from the human brain. In this work, we investigate how the dimensions of the sensing volume (the vapour cell) affect the performance of both a single OPM-MEG sensor and a multi-sensor OPM-MEG system. We consid...
Article
This paper presents a novel transcranial magnetic stimulation (TMS) pulse generator with a wide range of pulse shape, amplitude, and width. Approach: The novel MM-TMS device is the first to use a modular multi-level circuit topology at full TMS energy levels. It consists of ten cascaded H-bridge modules, each implemented with insulated-gate bipol...
Article
Full-text available
Background Transcranial magnetic stimulation (TMS) coils allow only a slow, mechanical adjustment of the stimulating electric field (E-field) orientation in the cerebral tissue. Fast E-field control is needed to synchronize the stimulation with the ongoing brain activity. Also, empirical models that fully describe the relationship between evoked re...
Article
Full-text available
Background Transcranial magnetic stimulation (TMS) allows non-invasive stimulation of the cortex. In multi-locus TMS (mTMS), the stimulating electric field (E-field) is controlled electronically without coil movement by adjusting currents in the coils of a transducer. Objective To develop an mTMS system that allows adjusting the location and orien...
Preprint
Full-text available
Background Transcranial magnetic stimulation (TMS) allows non-invasive stimulation of the cortex. In multi-locus TMS (mTMS), the stimulating electric field (E-field) is controlled electronically without coil movement by adjusting currents in the coils of a transducer. Objective To develop an mTMS system that allows adjusting the location and orien...
Preprint
Objective: This article presents a novel transcranial magnetic stimulation (TMS) pulse generator with a wide range of pulse shape, amplitude, and width. Approach: Based on a modular multilevel TMS (MM-TMS) topology we had proposed previously, we realized the first such device operating at full TMS energy levels. It consists of ten cascaded H-bridge...
Preprint
Full-text available
Background: The electric field orientation is a crucial parameter for optimizing the excitation of neuronal tissue in transcranial magnetic stimulation (TMS). Yet, the effects of stimulus orientation on the short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) paradigms are poorly known, mainly due to significant techn...
Preprint
Full-text available
Background Transcranial magnetic stimulation (TMS) coils allow only a slow, mechanical adjustment of the stimulating electric field (E-field) orientation in the cerebral tissue. Fast E-field control is needed to synchronize the stimulation with the ongoing brain activity. Also, empirical models that fully describe the relationship between evoked re...
Article
Many different types of TMS coils have been proposed and implemented, but all share certain common features. The induced electric field is always maximum in the superficial parts of the brain, nearest the coil, and attenuates toward the center of the head. Power requirements are high. Design tradeoffs are present between specific coil features incl...
Article
This work aims to reduce the acoustic noise level of transcranial magnetic stimulation (TMS) coils. TMS requires high currents (several thousand amperes) to be pulsed through the coil, which generates a loud acoustic impulse whose peak sound pressure level (SPL) can exceed 130 dB(Z). This sound poses a risk to hearing and elicits unwanted neural ac...
Article
Full-text available
In transcranial magnetic stimulation (TMS), the initial cortical activation due to stimulation is determined by the state of the brain and the magnitude, waveform, and direction of the induced electric field (E-field) in the cortex. The E-field distribution depends on the conductivity geometry of the head. The effects of deviations from a spherical...
Chapter
Transcranial magnetic stimulation (TMS) is a noninvasive method for focal brain stimulation, with applications in research, diagnostics, and treatment. In basic research, TMS can help establish a causal link between a brain circuit and a behavior. Clinically, repetitive TMS can alter the long-term excitability of specific brain regions to treat psy...
Preprint
Objective: This work aims to reduce the acoustic noise level of transcranial magnetic stimulation (TMS) coils. TMS requires high currents (several thousand amperes) to be pulsed through the coil, which generates a loud acoustic impulse whose peak sound pressure level (SPL) can exceed 130 dB(Z). This sound poses a risk to hearing and elicits unwante...
Article
Full-text available
Background Accurate data on the sound emitted by transcranial magnetic stimulation (TMS) coils is lacking. Methods We recorded the sound waveforms of seven coils with high bandwidth. We estimated the neural stimulation strength by measuring the induced electric field and applying a strength–duration model to account for different waveforms. Resul...
Preprint
In transcranial magnetic stimulation (TMS), the initial cortical activation due to stimulation is determined by the state of the brain and the magnitude, waveform, and direction of the induced electric field (E-field) in the cortex. The E-field distribution depends on the conductivity geometry of the head. The effects of deviations from a spherical...
Article
Background: Computational simulations of the E-field induced by transcranial magnetic stimulation (TMS) are increasingly used to understand its mechanisms and to inform its administration. However, characterization of the accuracy of the simulation methods and the factors that affect it is lacking. Objective: To ensure the accuracy of TMS E-fiel...
Article
Full-text available
Transcranial magnetic stimulation (TMS) is often targeted using a model of TMS-induced electric field (E). In such navigated TMS, the E-field models have been based on spherical approximation of the head. Such models omit the effects of cerebrospinal fluid (CSF) and gyral folding, leading to potentially large errors in the computed E-field. So far,...
Article
Full-text available
Short-interval intracortical inhibition (SICI) has been studied with paired-pulse transcranial magnetic stimulation (TMS) by administering two pulses at a millisecond-scale interstimulus interval (ISI) to a single cortical target. It has, however, been difficult to study the interaction of nearby cortical targets with paired-pulse TMS. To overcome...
Article
Full-text available
Chronic neuropathic pain is known to alter the primary motor cortex (M1) function. Less is known about the normal, physiological effects of experimental neurogenic pain on M1. The objective of this study is to determine how short-interval intracortical inhibition (SICI) is altered in the M1 representation area of a muscle exposed to experimental pa...
Preprint
Background: Accurate data on the sound emitted by various transcranial magnetic stimulation (TMS) coils is lacking. Methods: We recorded the coil sound waveforms of seven coils. We estimated the neural stimulation strength by measuring the induced electric field and applying a strength-duration model to account for different waveforms. Results: At...
Article
Mechanisms underlying short-interval intracortical inhibition (SICI) and facilitation (SICF) in the motor cortex seem to be sensitive to conditioning- pulse orientation. Available devices require manual coil rotation to adjust the electric field orientation, making it impractical to apply two consec- utive pulses with different orientations in milli...
Preprint
Full-text available
Background: Transcranial magnetic stimulation (TMS) is often targeted using a model of TMS-induced electric field (E). In such navigated TMS, the E-field models have been based on spherical approximation of the head. Such models omit the effects of cerebrospinal fluid (CSF) on the E-field, leading to potentially large errors in the computed field....
Preprint
Background: Computational simulations of the E-field induced by transcranial magnetic stimulation (TMS) are increasingly used to understand its mechanisms and to inform its administration. However, characterization of the accuracy of the simulation methods and the factors that affect it is lacking. Objective: To ensure the accuracy of TMS E-field s...
Poster
Introduction: Chronic neuropathic pain is known to induce plasticity in the motor cortex. We investigated whether also an experimental pain (short-lasting cold pain) induce plastic effects by studying short-interval intracortical inhibition (SICI) in the primary motor cortex (M1) in the cortical representation area of the hand exposed to experiment...
Article
State-of-the-art noninvasive electromagnetic recording techniques allow observing neuronal dynamics down to the millisecond scale. Direct measurement of faster events has been limited to in vitro or invasive recordings. To overcome this limitation, we introduce a new paradigm for transcranial magnetic stimulation. We adjusted the stimulation wavefo...
Article
Background: Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation method: a magnetic field pulse from a TMS coil can excite neurons in a desired location of the cortex. Conventional TMS coils cause focal stimulation underneath the coil centre; to change the location of the stimulated spot, the coil must be moved over the new...
Article
Background: Transcranial magnetic stimulation (TMS) allows focal, non-invasive stimulation of the cortex. A TMS pulse is inherently weakly coupled to the cortex; thus, magnetic stimulation requires both high current and high voltage to reach sufficient intensity. These requirements limit, for example, the maximum repetition rate and the maximum nu...
Preprint
Full-text available
The efficacy of transcranial magnetic stimulation (TMS) is determined by the magnitude and direction of the induced electric field in the cortex. The electric field distribution is influenced by the conductivity structure, in particular, the size of the head and the shapes of conductivity boundaries. We show that neglecting the head size can result...
Article
Full-text available
We investigate the electromagnetic properties of assemblies of nanoscale ϵ-cobalt crystals with size range between 5 to 35 nm, embedded in a polystyrene matrix, at microwave (1-12 GHz) frequencies. We investigate the samples by transmission electron microscopy imaging, demonstrating that the particles aggregate and form chains and clusters. By usin...
Article
In transcranial magnetic stimulation (TMS), we are interested in calculating the TMS-induced electric field (E-field), which defines the given stimulus. This is known as the forward problem, and there exist no general analytic solution for it. This is because the electric field is dictated by Maxwell’s equations, which are partial differential equa...
Article
The effect of transcranial magnetic stimulation (TMS) on the brain depends on the focality of the induced electric field (E-field). However, with commercial TMS coils, it is typically not known precisely how the E-field behaves as a function of distance from the coil. Our aim was to develop an automatic, computer-controlled calibrator for measuring...

Network

Cited By

Projects

Project (1)
Project
We develop new technology for TMS to further improve targeting accuracy, pulse-shape control, and closed-loop target and timing adjustment based on real-time feedback, e.g., from EEG or EMG measurements.