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closeIpsilateral activation by vibrotactile stimuli
Posted by Lior on 08 Jan 2007 at 08:18 GMT
Just a brief comment on the following sentence provided in the discussion section (p. 7) of this fascinating article:
"If the second of two periodic vibrations is presented on the opposite hand, it will engage a new and unadapted population of SI neurons in the opposite hemisphere, causing discrimination thresholds to be higher."
This assertion is supposedly based on the assumption that the ipsilateral SI is not engaged in processing a given vibrotactile stimulus. However, Palva et al. [1] have reported phase locking of the ipsilateral SI, in the theta and alpha frequency ranges, reaching significance ~160-300 ms of stimulus onset (see figure 5 at [1]). This finding suggests that the ipsilateral SI is also harnessed to process an incoming vibrotactile stimulus, to a lesser degree than the contralateral SI. As suggested by Dr. Harris via email, a more correct statement might be:
"If the second of two periodic vibrations is presented on the opposite hand, it will engage a *relatively* unadapted population of SI neurons in the opposite hemisphere, causing discrimination thresholds to be higher."
So much pedantry for this morning :-)
Regards,
Lior Golgher
[1] http://dx.doi.org/10.1523...
RE: Ipsilateral activation by vibrotactile stimuli
Justin_Harrris replied to Lior on 11 Jan 2007 at 05:17 GMT
The study by Palva et al (2005) does indeed report evidence of activity within the ipsilateral SI during weak electrotactile stimulation. As Lior notes, such activity (if it were also present in our experiments) could produce some adaptation among neurons within the ipsilateral SI. However, it is worth noting that the ipsilateral activity recorded by Palva et al was substantially weaker than that observed in the contralateral SI. Therefore, while it remains possible that the first vibration in our experiments may have induced some adaptation among the ipsilateral neurons, this should be much less than that in contralateral SI. Thus the difference in frequency discrimination thresholds between same-finger and opposite-finger comparisons would still reflect different levels of adaptation between ipsilateral and contralateral SI neurons.