fMRI Group

moving brain

Introduction

Multiple spontaneous rhythms exit in our brain even when we are doing nothing, or at resting state, such as rhythms of emotion, perception, memory…etc. However, how they functionally connect each other and synthesize the conscious/unconscious symphonies remains an unsolved question to modern neuroscientists. Traditional methodologies in exploring the functional connectivity emphasize on the task manipulations and take the spontaneous activity as internal noise. Nevertheless, several studies implied that the spontaneous activity might be an important role by providing the endogenous constraints in neural assemblies. Recently, the functional connectivity between multiple symmetric brain regions were consistently reported using the typical functional magnetic resonance imaging (fMRI) technique at the resting state, with which the interactions between brain regions can be observed without subjects’ task-performances. Not only does it contain the advantage of brain connectivity information under “task-free” procedure, especially for patients who are almost unable to perform tasks, the resting-state fMRI technique also provides the capability of longitudinal observation, which is essential as well in pathological and/or long-term cognitive issue.

Since the unique importance of the resting-state fMRI was addressed explicitly, proliferating application studies were disclosed to the neuroscience field. However, most of these application studies only provided the observations of chronic variations along with diseases without understanding the underlying physiology. Therefore, we are going to study the underlying neuron-vasculature mechanism of the functional connectivity from both electrophysiological and hemodynamic perspectives during the resting state. With the simultaneous recording of EEG/fMRI signal, the sources of the functional connectivity shall be clarified sophisticatedly with extraordinary spatial and temporal resolutions. Besides, for overcome the non-quantifiable and over-simplified features of current functional connectivity analysis, another goal of us is to develop advanced technologies in widening the physiological scope and sharpening the analyses process.

Research Topic

Quantified fMRI Techniques

Magnetic Resonance Imaging (MRI) provides superior images with high contrast of soft tissues and spatial resolution and is widely used in clinical practices. In the past decade, Functional MRI (fMRI) is often used to explore the brain function by detecting the hemodynamic change induced by specified cognitive or sensorimotor tasks.

However, traditional Blood Oxygenation Level Dependent (BOLD) fMRI technique contains complicated influences from cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral metabolic rate of oxygenation (CMRO2). It is difficult to achieve the quantification of parameters and the intra-subject comparison. Therefore, other non-invasive fMRI techniques based on CBF-weighted and CBV-weighted contrasts were developed recently. For example, FAIR and VASO fMRI techniques utilize the adiabatic inversion recovery radiofrequency pulse to label the blood outside the imaging region. Image subtraction or special parameter selection were used to acquire CBF or CBV contrast which reflects neural activation. The major objective of this dissertation is to develop and optimize FAIR and VASO techniques, and also to compare with traditional BOLD fMRI. With detecting of T1 value in each voxel, we can obtain the quantified value of regional CBF and its time-course variation.

Resting fMRI

Multiple spontaneous rhythms are present in our brain even when we are doing nothing, or at a resting state, such as rhythms of emotion, perception, memory…etc. However, how they functionally connect with each other and synthesize the conscious/unconscious symphonies remains as an unsolved question to the modern neuroscientists. Traditional methodologies in exploring the functional connectivity emphasize on the task manipulations and take the spontaneous activity as internal noise. Nevertheless, several studies implied that the spontaneous activity might have an important role by providing the endogenous constraints in neural assemblies. Recently, the functional connectivity between multiple symmetric brain regions were consistently reported using the typical functional magnetic resonance imaging (fMRI) technique at the resting state, with which the interactions between brain regions can be observed without engaging task-performance of a subject. Not only does it contain the advantage of brain connectivity information under a “task-free” procedure, especially for patients who are almost incapable of so-doing, the resting-state fMRI technique also allows the capability of longitudinal observation, which is essential to resolve some critical pathological and/or cognitive issue.

NTUtemplate

Montreal Neuroscience Institute (MNI) brain template, bases on Talairach coordinate, is used widely in fMRI researches around the world. However, the difference or distortion between MNI brain template and the averaged Chinese brain may lead to mismatch issue in functional neuroimaging among Taiwanese subjects. Therefore, we developed a novel Taiwanese NTU brain template (NTUtemplate) to solve this mismatch issue (n=120). Using optimized Modified Driven Equilibrium with Fourier Transform (MDEFT) gradient-echo sequence, high quality 3D T1-weighted MR images with high gray-and-white-matter contrast could be obtained in a reasonable resolution (1.0 x 1.0 x 1.0 mm3).

See detail: NTU Standard Brain Template

Deep Brain Stimulation

The MRI-compatible microelectrode array was bonded onto a long polyimide-based cable with pins soldered into two rows of 8 in a wide Dual-Inline Pin (DIP) format. The MRI-compatible microelectrode array was constructed with integrated connector pads, a long shaft and recording sites with spacing at 66-m interval (Figure 2-8A). The impedance of the 16 electrodes on the microelectrode array, measured by impedance spectroscopy, was approximately 250 kΩ at 100 Hz, and 800 kΩ at 1 kHz, respectively. The punctured tracts were clearly found in MR coronal and sagittal images of rat brain as shown in Figure 2-8B and Figure 2-8C, respectively. These MR images with implanting microelectrode array reveled less susceptibility artifact. Furthermore, histological section of rat brain was shown the lesion tract caused by microelectrode array implanting (Figure 2-8D). Multi-units were recorded in the VPM/VPL and evoked by air-puff stimulation on whisker, forepaw (FP) and hind-paw (HP).

Single unit was isolated from multi-unit from 16 channels. The FP stimulation was mostly represented in deeper locations (channel 1 to channel 8) and whisker were represented in shallow locations (channel 8 to channel 16). We could not found any unit response from HP stimulation (Figure 2-9C). According to the information that described above, 16 channels were partitioned into four parts (deep: channel 1- 4; mid-deep: channel 5-8; mid-top: channel 9-12; top: channel 13-16) for bipolar stimulation that delivered between the anode (+) and cathode (–) (Figure 2-9A). Figure 2-9B showed that brain activation maps were detected in the ipsilateral primary forelimb somatosensory (S1FL) and primary somatosensory barrel field (S1BF) through a direct VPM/VPL stimulation (200 A, 0.4 ms, 3Hz). Different locations of stimulation were evoked different responses in cortical areas. Locations of stimulation at bottom and mid-bottom were induced robust activation in the ipsilateral S1FL. At mid-top and top were induced robust and strong activation in the ipsilateral S1FL and S1BF, small number activation were found in the contralaterl S1FL and S1BF. These results indicated that the responses evoked by MRI-compatible microelectrode array were accord with sensory representation in the VPM/VPL.

Simultaneous Recording

To achieve both high temporal and spatial resolution to well understand the organization and interaction of cortex in brain network, it is obvious that the combination of EEG/fMRI modalities is a very attractive aim in neuroscience. As similar to the EEG and fMRI protocols described on previous paragraphs, all subjects will be asked to wear a multiple channel electrode cap for EEG, connecting with one MRI-compatible amplifier, receiving fMRI scans, and simultaneously recording the EEG signal for around six minutes. The systems are specifically designed for electrophysiological study inside the MRI scanner. Careful selections of conductors and RF-shielded equipment would help minimize interference to the images.

In the correlation between fMRI data and EEG signal (n=20), BOLD fluctuations of different brain areas show high correlation with different frequency bands as normal resting-state. However, as half eye-field visual stimulation given, the fluctuation of power value from gamma band shows the best synchronization with the hemodynamic BOLD signal. The gamma usually occurs during sensory processing and this result may show the evidence that BOLD signal has some links with the EEG fluctuations.

Laser Acupuncture

Many papers investigate the biological models of acupuncture. As Shang proposed, the mechanism of acupuncture may concern the nervous system, the cir- culatory system and other physiological systems. Dhond et al. recently found that following verum, but not sham, acupuncture, there was increased resting functional connectivity between specific brain areas and the default mode network (DMN), a network of brain regions more active during a nontask processing state. Somehow, those studies pertaining to resting functional connectivity have a key idea similar to the meridian system of acupuncture in traditional Chinese medicine. The so-called functional connectivity is to observe that these brain regions are thought to possess dynamic, synchronized oscillations.

Despite many published studies concerning LLLT, no work has been done comparing different modulated stimu- lation on the same acupoint in one experiment. This work has been investigated with EA [11, 20–22]. This paper aims to inspect whether laser with a mechanism distinct from electrical stimulation would produce a similar phenomenon. According to the ancient TCM book, Nan Jing (Classic of Difficulties), the acupoint, K1 (Yongquan), is one of the Well (Jing) points. In clinical practice, stimulation K1 has the effects of curing insomnia, poor memory and mania, and so forth. The acupoint K1 is an important acupoint for humans, but less attention has been given to it in recent researches. From Whittaker’s review of 30 laser acupuncture articles [12], modulated and nonmodulated treatments are often used alternately in these related studies. According to Han’s report [21], opioid peptides and opioid receptors involved in analgesia are elicited by electroacupuncture of different frequencies. In low frequency (less than decade Hz), enkephalins release more efficiency; on the contrary in high frequency (up above decade Hz), dynorphins release more efficiency. At 10 Hz, the intermediate frequency, there is a mediate secretion at both of those neuropeptides. Further, Lee’s study of 10 Hz external stimulation by sound or flash light can easily induce the somatic sensory so- called deqi in human beings [24]. Deqi is a big issue for acupuncture treatment of TCM. That is why we compare the 10-Hz-modulated Laser therapy with continued one. Therefore, we use LLLT to stimulate K1 (Yongquan) acupoint and observe the related human activations of the human brain.

The aim of this study is to compare the distinct cerebral activation with continued wave (CW) and 10Hz-modulated wave (MW) stimulation during low-level laser acupuncture. Functional magnetic resonance imaging (fMRI) studies were performed to investigate the possible mechanism during laser acupuncture stimulation at the left foot’s yongquan (K1) acupoint. There are 12 healthy right-handed volunteers for each type of laser stimulation (10-Hz-Modulated wave: 8 males and 4 females; continued wave: 9 males and 3 females). The analysis of multisubjects in this experiment was applied by random-effect (RFX) analysis. In CW groups, significant activations were found within the inferior parietal lobule, the primary somatosensory cortex, and the precuneus of left parietal lobe. Medial and superior frontal gyrus of left frontal lobe were also aroused. In MW groups, significant activations were found within the primary motor cortex and middle temporal gyrus of left hemisphere and bilateral cuneus. Placebo stimulation did not show any activation. Most activation areas were involved in the functions of memory, attention, and self-consciousness. The results showed the cerebral hemodynamic responses of two laser acupuncture stimulation modes and implied that its mechanism was not only based upon afferent sensory information processing, but that it also had the hemodynamic property altered during external stimulation.

Spontaneous Brain Oscillations

Non-task brain fMRI possesses oscillations and complex networks across cerebral hemispheres and specific areas (Achard, Salvador, Whitcher, Suckling, & Bullmore, 2006), and this functional connectivity has strong relationship, although not necessarily direct, with structural connectivity (Honey, et al., 2009). As a result, corpus callosotomy causes striking loss of resting inter-hemispheric BOLD correlations (Johnston, et al., 2008). Because axons extend outside the brain, if resting-state functional connectivity depends on intact nerve fibers, BOLD correlations should also exist outside the brain, for example, the limbs. And it should be different from the corticomuscular coherence, which exists during active or pathological muscle contraction (Mima & Hallett, 1999; Timmermann, Gross, Kircheis, Haussinger, & Schnitzler, 2002). The study supported the notion that brain spontaneous oscillations might spread outside of the brain, possibly through its fibers, synapses, and neuromuscular junction, and these oscillations could be detected under non-task and non-motion period. In addition, this connectivity seemed to oscillate within slower frequency band. Although FC in the auditory, visual, and sensorimotor cortices is characterized predominantly by frequencies slower than those in the cardiac and respiratory cycles (Cordes, et al., 2001), more thoughtful experiments and more subjects are needed to verify these interesting findings.

Large Scale Functional Brain Network Reorganization During Taoist Meditation

Members

PH.D. Student

湯依寧

email:fifitang@me.ee.ntu.edu.tw
website:
topic: fMRI
published : none
許艾伶

email: d01945001@ntu.edu.tw
website:
topic: Resting-state fMRI
published :
曾偉倫

email:puddingj@gmail.com
website:
topic: fMRI
published : none
吳虹誼

email:w610520@gmail.com
website:
topic: fMRI
published : none

Alumni

huangyunan.jpg黃筠安 YunAn Huang

email: hyapublic@gmail.com
website: none
topic: game fMRI
published : none
李家瑋 Chia-Wei Li

email: ffiln@me.ee.ntu.edu.tw
website:
topic: Resting-state fMRI, ASL
published :
liyichia01.jpg李宜家 YiChia Li

email: yichiali@me.ee.ntu.edu.tw
website: none
topic: Resting-state fMRI
published : none
林敏玲 Min-Ling Lin

email: asab0978@hotmail.com
website:
topic: Resting-state fMRI
published :

Research

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