Risto J Ilmoniemi

Risto J Ilmoniemi
Aalto University · Department of Neuroscience and Biomedical Engineering

Distinguished Professor

About

481
Publications
96,759
Reads
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30,916
Citations
Citations since 2016
120 Research Items
10220 Citations
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Introduction
I develop ways to measure, understand, and influence the brain using MEG, EEG, and TMS. In 1980's, I developed MEG devices and solutions to the MEG/EEG forward & inverse problems (aaltodoc.aalto.fi/handle/123456789/15355). In 1990's, I introduced navigated TMS and TMS-EEG; I founded Nexstim Plc to commercialize these. In 2008-12, I led an EU project to develop hybrid MEG-MRI; this continued as FET Open BREAKBEN project (2016–19) and EU Innovation Launchpad and Business Finland (2019-21) projects. I now aim at multi-locus TMS with closed-loop operation, funded by the Academy of Finland, Erkko Foundation (mTMS within fMRI magnet) and ERC Synergy (ConnectToBrain project with Gian Luca Romani and Ulf Ziemann). My ambition is to understand the physics of the brain and mind, guided by logic.
Additional affiliations
January 2017 - July 2017
Aalto University
Position
  • Head of Department
January 2012 - December 2016
Aalto University
Position
  • Professor
Description
  • NBE was formed on Jan. 1, 2015 as a result of a merger between the former Department of Biomedical Engineering and Computational Science and the Brain Research Unit of O.V. Lounasmaa Laboratory (former Low Temperature Laboratory)
January 2006 - present
Aalto University
Position
  • Professor of Applied Physics
Education
August 1981 - August 1985
Helsinki University of Technology (now Aalto University)
Field of study
  • Neuromagnetism

Publications

Publications (481)
Article
MOTOR and visual cortices of normal volunteers were activated by transcranial magnetic stimulation. The electrical brain activity resulting from the brief electromagnetic pulse was recorded with high-resolution electroencephalography (HR-EEG) and located using inversion algorithms. The stimulation of the left sensorimotor hand area elicited an imme...
Article
Full-text available
Doctoral Thesis, Department of Technical Physics, Helsinki University of Technology, Espoo, Finland. February 1985, Espoo, Finland.
Article
A 4-channel differential SQUID magnetometer has been built. Its design principles and construction are described. Proper matching of the detection coil to the SQUID input is discussed. Examples of auditory, dental pain and visual evoked response data are presented.
Article
A method of localizing brain activity by a new combination of magnetic and electrical recording, relative covariance, is described. The successful application of this method to alpha EEG is reported. Spontaneous human brain activity was recorded simultaneously with fixed scalp electrodes and a movable magnetometer. The analysis was restricted to th...
Article
Magnetoencephalography provides a new dimension to the functional imaging of the brain. The cerebral magnetic fields recorded noninvasively enable the accurate determination of locations of cerebral activity with an uncompromized time resolution. The first whole-scalp sensor arrays have just recently come into operation, and significant advances ar...
Article
Objective: Transcranial magnetic stimulation (TMS) induces an electric field (E-field) in the cortex. To facilitate stimulation targeting, image-guided neuronavigation systems have been introduced. Such systems track the placement of the coil with respect to the head and visualize the estimated cortical stimulation location on an anatomical brain i...
Article
Neuronal electroencephalography (EEG) signals arise from the cortical postsynaptic currents. Due to the conductive properties of the head, these neuronal sources produce relatively smeared spatial patterns in EEG. We can model these topographies to deduce which signals reflect genuine TMS-evoked cortical activity and which data components are merel...
Article
Background Spontaneous cortical oscillations have been shown to modulate cortical responses to transcranial magnetic stimulation (TMS). However, whether these oscillations influence cortical effective connectivity is largely unknown. We conducted a pilot study to set the basis for addressing how spontaneous oscillations affect cortical effective co...
Article
Background Spontaneous cortical oscillations have been shown to modulate cortical responses to transcranial magnetic stimulation (TMS). However, whether these oscillations influence cortical effective connectivity is largely unknown. We conducted a pilot study to set the basis for addressing how spontaneous oscillations affect cortical effective co...
Article
Full-text available
Navigated transcranial magnetic stimulation (nTMS) is a widely used tool for motor cortex mapping. However, the full details of the activated cortical area during the mapping remain unknown due to the spread of the stimulating electric field (E-field). Computational tools, which combine the E-field with physiological responses, have potential for r...
Article
Full-text available
Background Transcranial magnetic stimulation (TMS) is widely used in brain research and treatment of various brain dysfunctions. However, the optimal way to target stimulation and administer TMS therapies, for example, where and in which electric field direction the stimuli should be given, is yet to be determined. Objective To develop an automate...
Article
Background The impact of transcranial magnetic stimulation (TMS) on cortical neurons is currently hard to predict based on a priori biophysical and anatomical knowledge alone. Lack of control of the immediate effects of TMS on the underlying cortex can hamper the reliability and reproducibility of protocols aimed at measuring electroencephalographi...
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...
Article
Full-text available
In this paper, we analyze spatial sampling of electro- (EEG) and magnetoencephalography (MEG), where the electric or magnetic field is typically sampled on a curved surface such as the scalp. By simulating fields originating from a representative adult-male head, we study the spatial-frequency content in EEG as well as in on- and off-scalp MEG. Thi...
Article
Full-text available
Objective . Coils designed for transcranial magnetic stimulation (TMS) must incorporate trade-offs between the required electrical power or energy, focality and depth penetration of the induced electric field (E-field), coil size, and mechanical properties of the coil, as all of them cannot be optimally met at the same time. In multi-locus TMS (mTM...
Preprint
Full-text available
Background: Spontaneous cortical oscillations have been shown to modulate cortical responses to transcranial magnetic stimulation (TMS). If not controlled for, they might increase variability in responses and mask meaningful changes in the signals of interest when studying the brain with TMS combined with electroencephalography (TMS–EEG). To addres...
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...
Article
Full-text available
Besides stimulus intensities and interstimulus intervals (ISI), the electric field (E-field) orientation is known to affect both short-interval intracortical inhibition (SICI) and facilitation (SICF) in paired-pulse transcranial magnetic stimulation (TMS). However, it has yet to be established how distinct orientations of the conditioning (CS) and...
Preprint
Full-text available
Background The impact of transcranial magnetic stimulation (TMS) on cortical neurons is currently hard to predict based on a priori biophysical and anatomical knowledge alone. This problem can hamper the reliability and reproducibility of protocols aimed at measuring electroencephalographic (EEG) responses to TMS. New Method We introduce and releas...
Preprint
Full-text available
Background Transcranial magnetic stimulation (TMS) is widely used in brain research and treatment of various brain dysfunctions. However, the optimal way to target stimulation and administer TMS therapies, for example, where and in which electric-field direction the stimuli should be given, is yet to be determined. Objective To develop an automate...
Preprint
Full-text available
Objective Coils designed for transcranial magnetic stimulation (TMS) must incorporate trade-offs between the required electrical power or energy, focality and depth penetration of the induced electric field (E-field), coil size, and mechanical properties of the coil, as all of them cannot be optimally met at the same time. In multi-locus TMS (mTMS)...
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
Full-text available
Transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG) is a non-invasive tool for studying brain connectivity and excitability. However, the EEG signals are often hindered by artifacts. Several signal-processing methods have been developed for correcting these artifacts offline. Yet, new promising EEG TMS applications, s...
Article
Full-text available
Experimental data have indicated that transcranial magnetic stimulation (TMS) has high spatial specificity. For instance, even a millimeter-scale movement of the TMS coil above the motor cortex can change the recorded response in peripheral muscles drastically. However, such a small coil displacement induces a cortical electric field that overlaps...
Article
Full-text available
Transcranial magnetic stimulation (TMS)-evoked potentials (TEPs) allow one to assess cortical excitability and effective connectivity in clinical and basic research. However, obtaining clean TEPs is challenging due to the various TMS-related artifacts that contaminate the electroencephalographic (EEG) signal when the TMS pulse is delivered. Differe...
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 handbook is currently in development, with individual articles publishing online in advance of print publication. At this time, we cannot add information about unpublished articles in this handbook, however the table of contents will continue to grow as additional articles pass through the review process and are added to the site. Please note...
Preprint
Full-text available
Transcranial magnetic stimulation (TMS)-evoked potentials (TEPs) allow one to assess cortical excitability and effective connectivity in clinical and basic research. However, obtaining clean TEPs is challenging due to the various TMS-related artifacts that contaminate the electroencephalographic (EEG) signal when the TMS pulse is delivered. Differe...
Preprint
Full-text available
Transcranial magnetic stimulation (TMS) can non-invasively induce both excitatory and inhibitory neuronal activity. However, the neurophysiological basis for both kinds of modulation remains elusive. In this study, with a controlled dosage over the 30-s interval, we elicited excitatory and inhibitory TMS modulations over the human primary motor cor...
Article
Full-text available
Background To probe the functional role of brain oscillations, transcranial alternating current stimulation (tACS) has proven to be a useful neuroscientific tool. Because of the excessive tACS-caused artifact at the stimulation frequency in electroencephalography (EEG) signals, tACS + EEG studies have been mostly limited to compare brain activity b...
Article
Full-text available
This article is based on a consensus conference, promoted and supported by the International Federation of Clinical Neurophysiology (IFCN), which took place in Siena (Italy) in October 2018. The meeting intended to update the ten-year-old safety guidelines for the application of transcranial magnetic stimulation (TMS) in research and clinical setti...
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
This chapter addresses the need for hybrid magnetoencephalography (MEG) and magnetic resonance imaging (MRI) systems. The importance of combining MEG with MRI was realized early. The most important benefit of MEG over the widely available electroencephalography (EEG) is its ability to locate brain activity. To relate the location coordinates to ind...
Article
Full-text available
We present a novel open-source Python software package, bfieldtools, for magneto-quasistatic calculations using current densities on surfaces of arbitrary shape. The core functionality of the software relies on a stream-function representation of surface-current density and its discretization on a triangle mesh. Although this stream-function techni...
Article
Full-text available
Surface currents provide a general way to model magnetic fields in source-free volumes. To facilitate the use of surface currents in magneto-quasistatic problems, we have implemented a set of computational tools in a Python package named bfieldtools. In this work, we describe the physical and computational principles of this toolset. To be able to...
Article
Background Motor mapping with navigated transcranial magnetic stimulation (nTMS) requires defining a “hotspot”, a stimulation site consistently producing the highest-amplitude motor-evoked potentials (MEPs). The exact location of the hotspot is difficult to determine, and the spatial extent of high-amplitude MEPs usually remains undefined due to ME...
Preprint
Full-text available
Thermal motion of charge carriers in a conducting object causes magnetic field noise that interferes with sensitive measurements nearby the conductor. In this paper, we describe a method to compute the spectral properties of the thermal magnetic noise from arbitrarily-shaped thin conducting objects. We model divergence-free currents on a conducting...
Preprint
Full-text available
In this paper, we analyze spatial sampling of electro- (EEG) magnetoencephalography (MEG), where the electric or magnetic field is typically sampled on a curved surface such as the scalp. Using simulated measurements, we study the spatial-frequency content in EEG as well as in on- and off-scalp MEG. The analysis suggests that on-scalp MEG would gen...
Article
Full-text available
Transcranial magnetic stimulation (TMS) protocols often include a manual search of an optimal location and orientation of the coil or peak stimulating electric field to elicit motor responses in a target muscle. This target search is laborious, and the result is user-dependent. Here, we present a closed-loop search method that utilizes automatic el...
Preprint
Full-text available
Surface currents provide a general way to model static magnetic fields in source-free volumes. To facilitate the use of surface currents in magneto-quasistatic problems, we have implemented a set of computational tools in a Python package named bfieldtools. In this work, we describe the physical and computational principles of this toolset. To be a...
Preprint
Full-text available
We present a novel open-source Python software package, bfieldtools, for magneto-quasistatic calculations with current densities on surfaces of arbitrary shape. The core functionality of the software relies on a stream-function representation of surface-current density and its discretization on a triangle mesh. Although this stream-function techniq...
Poster
Full-text available
Real-time information about the structural connections in the brain would be highly valuable when performing navigated transcranial magnetic stimulation (nTMS). This information can be obtained using diffusion MRI (dMRI) based tractography that can extract major structural connections in the brain, in-vivo and non-invasively. However, this has been...
Article
Full-text available
Magnetic fields associated with currents flowing in tissue can be measured non-invasively by means of zero-field-encoded ultra-low-field magnetic resonance imaging (ULF MRI) enabling current-density imaging (CDI) and possibly conductivity mapping of human head tissues. Since currents applied to a human are limited by safety regulations and only a s...