Andrey Zhdanov

A novel approach for documenting naming errors induced by navigated transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is widely used both in basic research and in clinical practice. TMS has been utilized in studies of functional organization of speech in healthy volunteers. Navigated TMS (nTMS) allows preoperative mapping of the motor cortex for surgical planning. Recording behavioral responses to nTMS in the speech-related cortical network in a manner that allows off-line review of performance might increase utility of nTMS both for scientific and clinical purposes, e.g., for a careful preoperative planning. Four subjects participated in the study. The subjects named pictures of objects presented every 2-3s on a computer screen. One-second trains of 5 pulses were applied by nTMS 300ms after the presentation of pictures. The nTMS and stimulus presentation screens were cloned. A commercial digital camera was utilized to record the subjects performance and the screen clones. Delays between presentation, audio and video signals were eliminated by carefully tested combination of displays and camera. An experienced neuropsychologist studied the videos and classified the errors evoked by nTMS during the object naming. Complete anomias, semantic, phonological and performance errors were observed during nTMS of left fronto-parieto-temporal cortical regions. Several errors were detected only in the video classification. nTMS combined with synchronized video recording provides an accurate monitoring tool of behavioral TMS experiments. This experimental setup can be particularly useful for high-quality cognitive paradigms and for clinical purposes.

Hybrid ultra-low-field MRI and magnetoencephalography system based on a commercial whole-head neuromagnetometer

Ultra‐low‐field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices for signal detection. Similarly, modern magnetoencephalography (MEG) systems use arrays comprising hundreds of superconducting quantum interference device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG‐MRI instrumentation based on a commercial whole‐head MEG device is described. The combination of ultra‐low‐field MRI and MEG in a single device is expected to significantly reduce coregistration errors between the two modalities, to simplify MEG analysis, and to improve MEG localization accuracy. The sensor solutions, MRI coils (including a superconducting polarizing coil), an optimized pulse sequence, and a reconstruction method suitable for hybrid MEG‐MRI measurements are described. The performance of the device is demonstrated by presenting ultra‐low‐field‐MR images and MEG recordings that are compared with data obtained with a 3T scanner and a commercial MEG device. Magn Reson Med, 2013.

MEG dual scanning: a procedure to study real-time auditory interaction between two persons

Social interactions fill our everyday life and put strong demands on our brain function. However, the possibilities for studying the brain basis of social interaction are still technically limited, and even modern brain imaging studies of social cognition typically monitor just one participant at a time. We present here a method to connect and synchronize two faraway neuromagnetometers. With this method, two participants at two separate sites can interact with each other through a stable real-time audio connection with minimal delay and jitter. The magnetoencephalographic (MEG) and audio recordings of both laboratories are accurately synchronized for joint offline analysis. The concept can be extended to connecting multiple MEG devices around the world. As a proof of concept of the MEG-to-MEG link, we report the results of time-sensitive recordings of cortical evoked responses to sounds delivered at laboratories separated by 5 km.

An Internet-Based Real-Time Audiovisual Link for Dual MEG Recordings.

Hyperscanning Most neuroimaging studies of human social cognition have focused on brain activity of single subjects. More recently, “two-person neuroimaging” has been introduced, with simultaneous recordings of brain signals from two subjects involved in social interaction. These simultaneous “hyperscanning” recordings have already been carried out with a spectrum of neuroimaging modalities, such as functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and functional near-infrared spectroscopy (fNIRS). Dual MEG Setup We have recently developed a setup for simultaneous magnetoencephalographic (MEG) recordings of two subjects that communicate in real time over an audio link between two geographically separated MEG laboratories. Here we present an extended version of the setup, where we have added a video connection and replaced the telephone-landline-based link with an Internet connection. Our setup enabled transmission of video and audio streams between the sites with a one-way communication latency of about 130 ms. Our software that allows reproducing the setup is publicly available. Validation We demonstrate that the audiovisual Internet-based link can mediate real-time interaction between two subjects who try to mirror each others’ hand movements that they can see via the video link. All the nine pairs were able to synchronize their behavior. In addition to the video, we captured the subjects’ movements with accelerometers attached to their index fingers; we determined from these signals that the average synchronization accuracy was 215 ms. In one subject pair we demonstrate inter-subject coherence patterns of the MEG signals that peak over the sensorimotor areas contralateral to the hand used in the task.

Quantifying the contribution of video in combined video-magnetoencephalographic ictal recordings of epilepsy patients

INTRODUCTION Magnetoencephalography (MEG) measures magnetic fields generated by neuronal currents. MEG is complementary to EEG. Considerable body of evidence indicates that ictal MEG recordings can provide useful information for pre-surgical evaluation of epilepsy patients alongside the more established long-term ictal video-EEG. Ictal MEG is recorded in some epilepsy surgery centers. However, a wider adoption of ictal MEG is hampered by lack of tools for synchronized video-MEG recording similar to those of video-EEG. METHODS We have augmented MEG with a synchronized behavioral video-recording system. To estimate its additional value in ictal recordings, we retrospectively analyzed recordings of 10 epilepsy patients with and without the video. RESULTS In six patients out of ten, adding the video substantially changed the resulting interpretations. In all six cases the effect was considerable: the number of detected seizures changed by more than 50%. CONCLUSIONS Synchronized video and audio recording capabilities are important for effective ictal MEG recordings of epilepsy patients.

Noise amplification in parallel whole-head ultra-low-field magnetic resonance imaging using 306 detectors.

In ultra‐low‐field magnetic resonance imaging, arrays of up to hundreds of highly sensitive superconducting quantum interference devices (SQUIDs) can be used to detect the weak magnetic fields emitted by the precessing magnetization. Here, we investigate the noise amplification in sensitivity‐encoded ultra‐low‐field MRI at various acceleration rates using a SQUID array consisting of 102 magnetometers, 102 gradiometers, or 306 magnetometers and gradiometers, to cover the whole head. Our results suggest that SQUID arrays consisting of 102 magnetometers and 102 gradiometers are similar in g‐factor distribution. A SQUID array of 306 sensors (102 magnetometers and 204 gradiometers) only marginally improves the g‐factor. Corroborating with previous studies, the g‐factor in 2D sensitivity‐encoded ultra‐low‐field MRI with 9 to 16‐fold 2D accelerations using the SQUID array studied here may be acceptable. Magn Reson Med 70:595–600, 2013.

Combination of MEG and MRI in one setup

R.J. Ilmoniemi, J. Dabek, F.-H. Lin, J.O. Nieminen, L.T. Parkkonen, P.T. Vesanen, K.C.J. Zevenhoven, A.V. Zhdanov, J. Luomahaara, J. Hassel, J. Penttila, J. Simola, A.I. Ahonen, and J.P. Makela Dept. Biomedical Engineering and Computational Science, Aalto University School of Science, Espoo, Finland; Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; Martinos Center, Massachusetts General Hospital, Charlestown, MA, United States; Elekta Oy, Helsinki, Finland; BioMag Laboratory, HUSLAB, Helsinki University Central Hospital, Helsinki, Finland; VTT Technical Research Centre of Finland, Espoo, Finland; Aivon Oy, Espoo, Finland

Helsinki VideoMEG Project: augmenting magnetoencephalography with synchronized video recordings

Graphical abstract