This is a continuation of post #220. I want to keep the body of it altogether, so what has already been done is reproduced with minor changes as needed:
I will try to keep it pithy, but drill down with enough detail to keep it interesting. You may read about things you haven't heard of before. It won't be perfect, I will do my best to keep it accurate. If anyone has more accurate or current information that I may overlook, please, add input as you see fit:
1. Bi-Directional synesthesia: definition
2.
http://en.wikipedia.org/wiki/Mri#Basic_MRI_scans"
3. http://en.wikipedia.org/wiki/EEG"
4.
http://en.wikipedia.org/wiki/Arterial_spin_labeling#Arterial_spin_labeling"
5. Recommend you open a new TAB in your browser and view:
http://www.youtube.com/watch?v=HVGlfcP3ATI"
6. Discuss 2007: http://eprints.ucl.ac.uk/2934/1/2934.pdf" fMRI, EEG
7. Discuss 2009: http://www.researchgate.net/profile/Maarten_Van_der_Smagt/publications/" EEG only
8. Discuss results of both papers, where they agree, disagree or produce different results.
The definition of bi-directional synesthesia is not set in stone. Parts of it are still to be proven conclusively. There is evidence based on these two studies, (and earlier studies listed in the references section of each paper) that suggest a more complete definition of bi-directional synesthesia be defined as:
1. (as referred to in the two papers above) applies to: (color->grapheme, or grapheme->color), with one stimulating the other, in either order, at an explicit (perceived) and implicit (person is not aware) level involving the following:
Upper: associators (in the minds eye) Attentional/inhibitory processes are involved (2009 T Gebuis et al.)
Lower: projectors (out in space) Attentional/inhibitory/perceptual processes are involved (2009 T Gebuis et al.)
Synesthetic experience can result from bottom up (lower:perceptual) AND top down (attentional/inhibitory) processes, OR from top down (upper:attentional/inhibitory) experiences only
2. fMRI Overview:
Functional MRI (fMRI) measures signal changes in the brain that are due to changing neural activity. The brain is scanned at low resolution but at a rapid rate (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via T*2 changes; this mechanism is referred to as the BOLD (blood-oxygen-level dependent) effect. Increased neural activity causes an increased demand for oxygen, and the vascular system actually overcompensates for this, increasing the amount of oxygenated hemoglobin relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue.
My take on this description is that fMRI is very good at capturing the location and "activation" or a signal, whereas EEG is more accurate, in time, at capturing the signals characteristics, frequency, duration, etc...
3. EEG Overview:
The electrical activity of the brain can be described in spatial scales from the currents within a single dendritic spine to the relatively gross potentials that the EEG records from the scalp, much the same way that economics can be studied from the level of a single individual's personal finances to the macro-economics of nations. Neurons, or nerve cells, are electrically active cells that are primarily responsible for carrying out the brain's functions. Neurons create action potentials, which are discrete electrical signals that travel down axons and cause the release of chemical neurotransmitters at the synapse, which is an area of near contact between two neurons. This neurotransmitter then activates a receptor in the dendrite or body of the neuron that is on the other side of the synapse, the post-synaptic neuron. The neurotransmitter, when combined with the receptor, typically causes an electrical current within the dendrite or body of the post-synaptic neuron. Thousands of post-synaptic currents from a single neuron's dendrites and body then sum up to cause the neuron to generate an action potential. This neuron then synapses on other neurons, and so on. EEG reflects correlated synaptic activity caused by post-synaptic potentials of cortical neurons.
and
EEG also has some characteristics that compare favorably with behavioral testing:
* EEG can detect covert processing (i.e., processing that does not require a response)
* EEG can be used in subjects who are incapable of making a motor response
* Some ERP components can be detected even when the subject is not attending to the stimuli
* As compared with other reaction time paradigms, ERPs can elucidate stages of processing (rather than just the final end result)
4. fMRI, EEG limitations:
Functional MRI has high spatial resolution but relatively poor temporal resolution (of the order of several seconds). Electroencephalography (EEG) directly measures the brain's electrical activity, giving high temporal resolution (~milliseconds) but low spatial resolution. The two techniques are therefore complementary and may be used simultaneously to record brain activity.
and
EEG has several strong points as a tool for exploring brain activity. EEG's can detect changes within a millisecond timeframe, excellent considering an action potential takes approximately 0.5-130 milliseconds to propagate across a single neuron, depending on the type of neuron[13]. Other methods of looking at brain activity, such as PET and fMRI have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., SPECT, fMRI)
5. Recommend you open a new TAB in your browser and view:
http://www.youtube.com/watch?v=HVGlfcP3ATI"
6. Discuss 2007: http://eprints.ucl.ac.uk/2934/1/2934.pdf" fMRI, EEG
My interpretation (from paper #1 above): when color stimulates number, the synesthete sees the number, and brain shows activation in color and grapheme areas. Here is the tricky part, at this point the person is not aware that the number (secondary stimulation) is stimulating the color area of the brain (they do not see it, it is implicit), experimental data shows a cross activation in the areas of the brain associated with grapheme and color areas. This is the implicit case: a synesthete compared the height of two lines, line color modulated the performance, a longer line was presented in a color that was induced by a larger digit. This is the congruent case.
There is another case as well. This is the explicit case: a synesthete compared a longer line appeared in a color induced by a smaller digit and a shorter line in a color that was induced by a larger digit. This is the incongruent condition. The synesthete subject spontaneously reported that the colors of the lines evoked the perception of the corresponding digits, showing explicit experience of bi-directionality.
7. Discuss 2009: http://www.researchgate.net/profile/Maarten_Van_der_Smagt/publications/" EEG only. Remember, you must sign up
here in order to download this paper.
We will see later that the implicit case supports evidence for 'higher" and "lower" synesthetes indicating that, excerpt from the 2009 paper, (I let the authors relate this information because it was clearer than my repeated attempts at interpretation, most important concepts highlighted in blue):
these results are indicative of the existence of distinct groups of synesthetes. Synesthetic experiences can apparently arise as a result of both bottom up (perceptual) and topdown (attentional⁄inhibitory) processes, or as a result of top-down (attentional⁄inhibitory) effects only. Our results fit well with the classification proposed by Ramachandran & Hubbard (2001), who suggested that besides the classification of synesthetes on the basis of their phenomenological experience, synesthetes could be classified on the basis of the inducers or the triggers of the synesthetic experience. They referred to synesthetes that reveal effects at lower perceptual processes as ‘lower’ synesthetes and to synesthetes with higher cognitive effects as ‘higher’ synesthetes. Our results indicate that attentional or inhibitory processes appear to play a role in bi-directional priming in all synesthetes, whereas only some (possibly ‘lower’) synesthetes reveal a priming effect at a lower, possibly perceptual level, as well. Dixon & Smilek (2005) already emphasized the necessity of scrutinizing effects at the single subject level. They stated that if synesthesia is not a unitary phenomenon, possible patterns might be masked when all synesthetes are grouped together, resulting in conflicting reports or erroneous conclusions. Our results underline this suggestion and might explain some of the conflicting results reported concerning the stage at which the synesthetic experience arises. Involvement of both early pre-attentive as well as later attentional processes has been demonstrated in psychophysical (see for a critical review, see Gheri et al., 2008) as well as imaging research (Paulesu et al., 1995; Schiltz et al., 1999; Nunn et al., 2002; Elias et al., 2003; Weiss et al., 2005; Rich et al., 2006; Barnett et al., 2008; Beeli et al., 2008; Brang et al., 2008). In accordance with the study of Hubbard et al. (2005), the present study demonstrated that (grapheme-color) synesthesia is far from a unitary phenomenon.
Our results demonstrate, for the first time, that the same mechanisms underlie bi-directional interactions in synesthesia, at least for implicit synesthetes. At the group level, the priming effect for number to color as well as color to number was present at parietal (possibly perceptual processes) as well as frontal electrode sites (possibly attention or inhibitory processes). The ERP-components affected did not differ Multiple dimensions in bi-directional synesthesia 1709
8. Discuss results of both papers, where they agree, disagree or produce different results.
I am a bit tired at this point, I think you have seen by now what an fMRI can detect versus an EEG, is that the newer 2009 Paper using strictly EEG measurements is that the "priming effect is definitely" more pronounced subjects with synesthesia versus those who do not have it: See figure below:
Second, the first paper (2007) using both fMRI and EEG (non-concurrent) produced evidence for both implicit and for the first time explicit bi-directional synesthesia. I have more to add but can't quite think straight now. No use in pushing and saying something stupid. I will add more here later before the edit period expires. Quote a lot of food for thought and review (if you read the papers three times like I did so most of it sinks in).
Rhody... :zzz:
P.S. I learned something about "learning" in this process that I never really paid attention to before. When you read and try to digest complex material, you never "get it" the first or even the second time through, suggesting as I have come to understand it, new "brain mapping" consisting of new long term neuronal connections being made in the brain when repeated attempts are made to grasp the material. I got this from "The brain that changes itself" by Norman Dodge, MD. Highly recommended reading by: V.S. Ramachandran, who is already at the top of my reading list, so it was a no-brainer from there. I plan to use some of the material from this book for future probings of the mysteries of the brain. There, now I am done, lol.
lol I hope not. There are more brain mysteries to be probed and discussed, at an even deeper level. I am working that now, to be posted in a new thread. This subject blew me away almost as much as synesthesia did a few months back, and from what I know so far is even newer than serious research being done in synesthesia. This time I will take my time before I post and provide as much background/research as I can.
