EEG - fMRI: Physiological Basis, Technique, and Applications
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Functional magnetic resonance imaging (fMRI) and Electronecephalography (EEG) are very important and complementary modalities since fMRI offers high spatial resolution and EEG is a direct measurement of neuronal activity with high temporal resolution. Interest in the integration of both types of data is growing rapidly as it promises to provide important new insights into human brain activity as it has already done so in the field of epilepsy. The availability of good quality instrumentation capable of providing interference-free data in both modalities means that electrophysiological and haemodynamic characteristics of individual brain events can be captured for the first time. Consequently, it seems certain that the integration of fMRI and EEG will play an increasing role in neuroscience and of the clinical study of brain disorders such as epilepsy.
The proposed book will discuss in detail the physiological principles, practical aspects of measurement, artefact reduction and analysis and also applications of the integration of fMRI and EEG. All applications, which are mainly in the fields of sleep research, cognitive neuroscience and clinical use in neurology and psychiatry will be reviewed.
modelling issues will be discussed in greater detail in this chapter. Interictal EEG–fMRI What Is an Interictal Spike? Epileptiform interictal EEG abnormalities include: spikes, which are fast electrographic transients lasting less than 70 ms; and sharp waves, which last 70–120 ms (de Curtis and Avanzini 2001). That these are pathological is supported by their very rare occurrence (<1%) in healthy individuals (Gregory et al. 1993), and their strong association with epilepsy (Marsan and Zivin
phenomena have been established: the spindles or waves between 7 and 14 Hz, also called sleep or sigma spindles, which appear at sleep onset, and the delta waves (1–4 Hz), which are paradigmatic of deeper stages of sleep. Steriade and his group in Quebec (see Sect. 2) described another very slow oscillation (0.6–1 Hz) in animals that is able to modulate the occurrence of different typical EEG sleep events, such as delta waves, sleep spindles and even short, high-frequency bursts. This very slow
generalised paroxysms seems to be related to different patterns of activation. Moeller et al. (2008b) demonstrated that, in six children with short generalised polyspike-and-wave paroxysms (PSWs), the neuronal network consisting of thalamic activation and deactivation in cortex and caudate nucleus may be observed several seconds (on average 6 s) before the onset of the discharges on scalp EEG—the early thalamic activation is followed by a cortical deactivation and then by a deactivation in the
been convincingly demonstrated that the amplitude of ERP components varies systematically over time, reflecting cognitive processes, and that this variation can be used to identify those brain regions where the BOLD contrast shows the same variation (Eichele et al. 2005). In a similar way, Benar et al. (2007) were able to demonstrate that the amplitude of P3 correlated positively with BOLD activity in the ACC, which is believed to reflect attentional processes. In addition, a negative correlation
the study were consistent with those of former studies supposing a frontoparietal involvement during retrieval success. In addition, the study demonstrated that parietal activity associated with retrieval success produced by deeply encoded items was greater than that produced by shallowly encoded items. However, functional discrepancies appeared: the correct recognition of items presented during the encoding task led to enhanced prefrontal activity compared to the repetition condition; instead,