empty thoughts VIII

1. handedness in mice seems to correlate with a lateralized dominance of dopamine expression; a mouse who prefers to use the left paw has a lower level of dopamine in the right hemisphere (Berneoud et al 1990) [which screws with my mind because in Parkinson's a mouse who has impairment of left paw control has lower levels of dopamine in the right hemisphere... fucking dopamine].

2. human fetuses suck their thumb beginning at the 15th week of gestation. of 75 fetuses who suck their thumbs, the 60 who suck their right thumb all become right handed teenagers. of the 15 who suck their left thumb, 5 become right handed and 10 become left handed (Cabib et al 1995) [so handedness is a developmental thing, not a consciousness thing?... in the vicinity of week 15 the brain is primarily ventricles, aka stem cell pockets, so what, are we talking about dimorphic differentiation as dictated by the notochord?].

3. whether early brain asymmetries contribute more to language development or handedness remains a challenging question (Corballis 2003) [which is damn sweet... that handedness might correlate with language centers, particularly Broca and Wernike's areas localized in the left hemisphere].

4. fibroblast growth factor 8 (FGF8) is secreted from the anterior cortex during development which might be distributed unevenly to the left and right cortical hemispheres, leading to asymetrical topography (Sun et al 2005) [i can't find any studies on whether or not this secretion occurs anywhere near gestation week 15 where striatum and cortex develop from the ventricle cells... and it is driving me mad].

5. normal brain asymmetry is disrupted in individuals with schizophrenia, autism, dyslexia, etc. (Herbert et al 2005; Hugdahl 1998; Falkai 1992) [does molecular regulation conjugate brain asymmetry and handedness?... do schizophrenics etc. demonstrate tendancies toward ambidexterity?!... do all these conditions correlate to oxygen deprivation during critical periods of gestation?!...].

6. 90% of the human population is right-hand dominant. of that population, 95% are also language skill dominant in the left hemisphere. of the remaining 10% who are left-handed, only 70% are language dominant in the left hemisphere (Sun and Walsh 2006).

Then... does handedness actually indicate a significant specialization in unilateral hemispheric function? The hand manipulates the environment, and the contralateral brain maps the sensory information into a model... but is the correlation between left-handedness and holistic, intuitive and musical function of the right brain as robust as it is imperfect? And for that matter, is 90% of the human population right handed in correlation with evolutionary utility of the left brain as a linear, language manipulating analytical tool?