Comments and ControversiesNeurophysiology of functional imaging
Introduction
Non-invasive brain imaging methods (i.e., PET and fMRI) have had tremendous success in localizing sensory functions. Using the simple differencing method, primary motor and sensory cortices can be reliably mapped with results matching those previously only found by invasive methods (Hubel and Wiesel, 1959, Wandell et al., 2007). For more complex mental functions, such as language, fMRI can show hemispheric dominance so reliably that it is now used to guide surgical decisions in patients with refractory epilepsy (Medina et al., 2007). These successes have encouraged scientists to use neuroimaging to address psychological questions in an effort to transform the contingent, subjective concepts of psychology and everyday life into communicable understandings with the objectivity of physical science.
Section snippets
Cognitive neuroimaging
In the earliest years of functional imaging, its main focus was on Neurophysiology so as to determine the regulation of cerebral metabolism and blood flow during brain function. The first SPECT and PET maps of brain activity in response to cognitive concepts were so beautiful that they raised hopes for exploring psychology (Lassen et al., 1978, Reivich et al., 1983). As PET and fMRI developed the ability to map responses to mental stimuli, the techniques became more widely used for experiments
The modularity concept
The philosophical problem of defining concepts of mental function was a primary concern of Ludwig Wittgenstein, who showed that only mathematical or logical terms can be unequivocally defined, whereas even simple terms like “chair” defy explanations that would identify all objects we regard as chairs and exclude all that we do not (Wittgenstein, 1953). Once we recognize that common objects cannot be defined with the rigor of logic, we realize how revolutionary it would be if words like “working
Delocalized activity
The difficulties besetting the modularity concept were seen in a wide range of fMRI experiments. It has become apparent that cortical activations in response to cognitive activity were widespread, being found in many regions, instead of being reproducibly localized as were the primary responses to sensory inputs. This dealt a blow to the hope that even though cognitive concepts might not strictly be defined by modules of brain functions; still brain localization would make concepts more
Negative BOLD
Cognitive Neuroscience in addition to assuming psychological modules had also postulated that the modules were operated on by a computer-like brain although the details of such processing had no consensus. The assumption of a computer-like brain was confounded by results showing that imaging signals observed in certain brain regions were rather consistently negative during stimulation (Shulman et al., 1997). By the time that negative BOLD signals became noteworthy, the role of cerebral
fMRI and energy based neuroscience
The combination of fMRI, 13C MRS, and electrophysiology has allowed the energy consumption of the many neurons in an fMRI voxel to be correlated with the electrical activity of ensembles of individual neurons in the same volume. Results from electrophysiological, fMRI, and 13C MRS experiments are expressed in terms of the fundamental physical parameter of energy consumption: the cerebral metabolic rate of oxygen consumption (CMRO2) since essentially all brain energy comes from the oxidation of
Effects of baseline energy on fMRI
To explore the neuronal foundations of baseline and incremental energetics, we conducted electrophysiological and fMRI studies in rats at two anesthetic states, characterized by very different baseline energies (Maandag et al., 2007); the lower energy state (α-chloralose) was 40–60% lesser than the higher energy state (halothane). Forepaw stimulation was administered in both states to excite the contralateral primary somatosensory cortex (S1). There were major differences between the two states
Empirical studies of brain function
The dynamic interplay between experimental results and scientific hypotheses described above reflects the excitement of science, the movement from one issue to the next that is raised in the course of study. In contrast to the assumptions of Cognitive Psychology that there were concepts of Mind in need of definition, we propose that mental activity can be studied by the reliable techniques of contemporary neurophysiology, certainly including fMRI and PET, without making revolutionary a priori
Shifting paradigm of psychological studies
The physiological studies of cerebral energetics combined with fMRI are profoundly changing the psychological interpretation of Cognitive Neuroimaging. Prominent early proponents of Cognitive Neuroscience, facing the growing experimental failings of modularity and cerebral localization, have been developing alternate descriptions of brain function that utilize neurophysiological results (Raichle and Mintun, 2006). In the past five years it would not be an exaggeration to say that the
Acknowledgments
This work was supported by NIH grants (R01 MH-067528, R01 DC-003710, R01 NS-037527, R01 NS-051854, P30 NS-52519). We thank Dr. Jennifer K. Roth for comments on the manuscript.
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2016, Clinical RadiologyCitation Excerpt :Currently, most researchers measure the relaxation rate (R2*), which is obtained from multiple-echo gradient-echo (GRE) sequences and is used as an indicator of tumour oxygenation.19,20 Although this technique has high spatial resolution (millimetre-sized) and good repeatability,21–23 the long acquisition time prevents it from keeping pace with rapid physiological changes. To date, some mathematical models and post-processing methods derived from T2* imaging techniques, such as relative oxygen extraction fraction (rOEF) mapping and T2 prime (T2′) imaging, have been used to quantify BOLD signals (qBOLD).24,25
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2013, NeuroImageCitation Excerpt :Therefore the increase in energy consumption during perceptual processing is very small compared to the resting energy consumption (Schölvinck et al., 2008). Since energy is a valuable commodity, these facts point to spontaneous activity as serving a vital function for the brain (Van Eijsden et al., 2009). It is certainly the case that coordinated spontaneous activity is always present at some level, taking different forms during different states of consciousness.
Odor representation in the olfactory bulb under different brain states revealed by intrinsic optical signals imaging
2013, NeuroscienceCitation Excerpt :This function is important not only for daily life and survival but also for higher brain functions, such as decision-making, planning, judgment, and the establishment of preferences that are proper for a given situation (Li et al., 2011). However, the brain itself is constantly modulated by both external and internal factors, such as circadian rhythms; aging; physical, physiological, and psychological factors; arousal; and metabolic conditions (Shulman et al., 2007; Fontanini and Katz, 2008; Tsuno et al., 2008; van Eijsden et al., 2009; Zhu et al., 2009). Therefore, determining how the sensory perception of the same stimulus is represented by the corresponding sensory system under different brain states is important for understanding the brain mechanisms that underlie sensory representations, which is attracting lots of attentions from the relevant fields (Li et al., 2011; Wilson et al., 2011; Kato et al., 2012; Vincis et al., 2012).
What does it mean to call chronic pain a brain disease?
2013, Journal of PainCitation Excerpt :Henry Beecher long ago noted that the same pathological lesions could produce overwhelming or minimal pain depending on the environment.2 This clinical issue echoes current concerns in the neuroimaging literature about whether psychological concepts and functions (like pain) can be associated with discrete localized brain regions independent of the environmental context within which they occur.29 Chronic pain depends not only on brain processes, but on personal processes and meanings as well.
Ongoing physiological processes in the cerebral cortex
2012, NeuroImageCitation Excerpt :On this last point, it is known that metabolic energy is a costly commodity in evolution, and the brain expends 20% of the body's energy despite accounting for only 2% of the body's mass. Approximately 80% of this expenditure is thought to be related to the maintenance of homeostasis (Hyder and Rothman, 2010; Raichle, 2006; van Eijsden et al., 2009). The contribution of spontaneous activity variation to the brain's resting energy consumption may be considerable, which further underscores the importance of understanding its essence.