Essay On Practical Investigation Of Mind And Body –

Positive Bold fMRI Response in Neuroimaging

Positive Bold fMRI Response in Neuroimaging and its Relation to Neural Activity
Introduction
Some research suggests that functional magnetic resonance imaging (fMRI) signals result from an indirect measure of neural activity. Interpreting these signals allows making deductions about the nervous system and requires some understanding of the signaling mechanisms according to Logothetis and Wandell (2004). The following academic discourse explores, reviews, and describes the literature aligned with the focus of this subject identifying research variable outcomes.

About Positive Bold fMRI Response

As a part of cognitive neuroscience, the fMRI proves a revolutionized aspect in the last decade. The process is a coupling of the neural movement in conjunction with local blood flow oxygenation (haemodynamics) taking place in the brain (Ogawa, Lee, Kay, and Tank, 1990). This function allows measurement of brain activity as a non-invasive localization medical procedure in order to determine the extent of a cognitive brain neural activity in research animal models (Logothetis and Wandell, 2004). Research shows how this provides for better understanding of both the function and the dysfunction of the human brains (Logothetis and Wandell, 2004; Aguirre, 2014; Amaro and Gareth, 2005; Attwell and Iadecola, 2002; Hyder et al, 2001; Heeger and Ress, 2002; Ugurbil, Toth, and Kim, 2003; Pernet, 2005; Logothetis, 2003; Schein, 2009; Menon and Seong-Gi, 1999).
The underlying neuronal movement and its relationship to the fMRI signal remains the key determinate of the success of the research. Limitations arise from the vascular blood source of the fMRI signal and its usefulness as a specific research technique. While studies provide how the metabolic stipulations for increased neuronal movement trigger the fMRI signals, nonetheless only partial understanding of the process exits. Consequently, this fact remains of critical importance to the research of neuroscience (Logothetis and Wandell, 2004).
In the existing literature on the research completed about the neural responses taking place with the fMRI neurophysiological experiments prove fraught with conflicting results exacerbates a definite need for understanding this relationship. The activity of the primary visual cortex (VI) connected to spatial attention and human ability in performing related discriminative tasks improves when cues exist to do so without having any need for eye movement related to the spatial loci of the particular stimulus as a cognitive process (Logothetis and Wandell, 2004).
The study of the brain remains a case of the more learned the more scientists don’t know as explained by Logothetis and Wandell (2004, p. 142) aligns to “some theories (that) posit that attention is mediated by selection very early in the visual pathways, attentional effects have been notoriously difficult to measure using single-unit electrophysiology in area V1 of the monkey brain.” At the same time, their literature explains, “By contrast, robust attentional effects have been readily measurable with fMRI in human V1 and attentional effects in extrastriate cortical areas (such as V4) (and) seem considerably larger in human fMRI experiments than in monkey electrophysiology experiments.” [Sic]
Accordingly, the question arises whether this results as a differentiation of species or in what the process measures. Further to this is questioning whether the signal projected by the fMRI reflects both the locally populated neural firing rates and the activity at the subthreshold level thus, existing as concurrent inhibition and excitation, or feedback from distant, higher planes of activity in the visual cortex such as modularity inputs thus, creating spikes in the readouts ((Logothetis and Wandell, 2004).
Additionally, interpreting the fMRI signal suggesting it as reflecting changes occurring in the synchronistic aspects of the neuron activity may suggest the lack of any increase of the mean firing rate according to the concomitant increase process. Further to the variety of conflicting outcomes of the research shows complications connected with fMRI signals reflecting large pooled movement among numerous neurons thus causing fMRI response modulation possibly due to larger firing rates within smaller sub-populated groups of neurons, or conversely smaller firing rates in larger numbered sub-populated groups of neurons (Logothetis and Wandell, 2004).
The fact remains these are only some of the examples that continue driving the research in better understanding of the relationship of fMRI signals resulting from an indirect measure of neural activity. In addition, the understanding the source of neuron based signals in affecting the measurement of it and the fMRI signals requires ongoing research. The literature provides the need for varied systematic experimental protocols in the continued research in the focus of understanding the relationship between these two. In studying about the relative measurements of both the neuronal and fMRI signals having a connection the research looks at single as well as multi-unit activity showing spiking. Literature suggests the benefit of neurophysiologists taking different approaches in better understanding fMRI. In their routine digitalization of the complete electrophysiological signal it is suggested moving from the current focus on just the spiking activity for determining whether specific circumstances or not, checking on the affect the decoupling from the outpour spiking movement of single units of the intra-cortical area neuronal activity. This is as connected to the low-pass filter (LFP) or on manipulation under anesthesia (MUA) in the process as described by Logothetis and Wandell (2004).
In addition, literature suggests the advantage .of comparing measurements among the local average firing rates with local synaptic activity averages because in this case due to the identification of synaptic activity as linked with metabolic needs of the process. Nonetheless, it remains unclear as to the manner of directly measuring the average synaptic movement. Further, review of the literature implies the benefit of outcomes of measuring fMRI signals when no spiking occurs as suggested in the case of the cortex activity cooling for determining the amount of the signal exists as a directed process of exclusively inducing inputs into the cortical area (Logothetis and Wandell, 2004).

Blood Oxygenation

Other literature in relation to the fMRI signal measures and the connection as earlier stated with the BOLD contrast MRI and neuronal activity aligns to tracking changes occurring in the blood oxygenation expectation in the use of anesthetic inhaled gases as well as from hypoglycemic insulin induced changes on the physiological changes occurring in animal research of cognitive brain processes. The balance of the blood flow supply affects the contrasting measurements because of the amount of oxygen it provides the brain and the brain ability to react neurologically. Normal conditions prove the blood remains fully oxygenated with no contribution affecting the BOLD contrast process. While conversely, any venous blood vessels with deoxygenated blood therefore, indeed contribute to dark lines in the imagery (Logothetis and Wandell, 2004).
Results found in research literature indicate the BOLD contrast as useful for real time noninvasive monitoring of the blood oxygenation levels in the brain areas responding to central nervous system drugs affecting blood flow or basal metabolism of the brain. Indications show enhanced BOLD-imagery contrast appears at high magnetic fields and the observed effect shows a similar field strength to the highest field strength currently used on humans Logothetis and Wandell, 2004).
Most tracer methods used in the MRI measurement differ from the BOLD contrast relies on the intrinsic image and contrast agent synchronized precisely to external stimuli providing good time related resolution imagery as outlined by Ogawa et al (1990, p. 9872). Thus, they find, “The underlying mechanisms of BOLD contrast (as it relates to the BOLD fMRI use as well) is the accentuation by gradient-echo imaging at high magnetic fields of effects produced by magnetic susceptibility variation that is caused by an endogenous paramagnetic agent.” The implication of the usefulness of this process as connected to the BOLD fMRI relationship to the neuron activity of the brain measurements therefore aligns to the use of this in the ongoing studies.
Others conducting research connect the BOLD effect of imaging in the functioning brain positing the need for interpreting the measurement as a direct neuronal signal reflection rather than as the locus of any increase of the use of energy in the brain. This result connects in processing occurring aside from the lack of any change in the brain using energy so the BOLD provides a signal that aligns to the same process of the cerebellum reflecting neural movement within the brain area in contrast to any input or output derived from that area (Atwell and Iadecola, 2002).
This shows no net change of energy usage as connected to the neural processing possibly leading to a BOLD signal that also influences changes in neural spike output without any change in the signal systems that control blood flow as potentially failing in generating a BOLD signal. While sites of increased neural activity may regularly combine with other areas of neural movement, localizing increased metabolic process. Therefore, this suggests there exists in the process of the BOLD response is an issue with the neural signal rather than any related to a problem with energy (Atwell and Iadecola, 2002).
As provided at this point of the examination, review, and assessment of the literature among other studies relating to BOLD fMRI measurement connected to neural activity in the cognitive areas of the brain the view tales a pragmatic approach. This reflects around the value of maintaining as Raichle (1998, p. 3961) suggests as “a sense of proportion when it comes to viewing functional imaging signals (and points to how) the average adult human (brain) represents” approximately 2 percent of the total body weight. Regardless, of its small size compared to other parts of the body it uses 20 percent of the oxygen consumed by the body. Thus in relation to other suggested implications presented in this discourse connected the ongoing search for understanding the connection to the BOLD fMRI and neural activity in the brain in the cognitive processes there exists contrasts in the findings.

Conclusion

As posited in the introduction of this scholastic examination, the subject looked at the existing research showing that BOLD fMRI signals result from an indirect measure of neural activity. The sum of the assessment of the research findings looks at the abundance of contrasts in the findings on the subject that definitely prove there is no solid one truth about what is the exact relationship of how the connection to the neural activity affects the MRI signals. Further, this relates to the amount of oxygen carried to the brain and its effect on the neural connection activity.

References

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Hyder, F. et al. 2001. Quantitative functional imaging of the brain: towards mapping neuronal activity by BOLD fMRI. NMR Biomed., 14: pp. 413–431
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Menon, R, and Seong-Gi Kim. 1999. Spatial and temporal limits in cognitive neuroimaging with fMRI. TICS 3(6), 207-216.
Ogawa, S., Lee, T. M., Kay, A. R., Tank, D. W. (1990). Brain magnetic resonance imaging with contrast dependent on blood oxygenation. Proceedings of the National Academy of Sciences USA, 87:9868-9872.
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