Einstein and Taung: two brains collide
Dean Falk has a new article in the journal Brain, in which she and collaborators uncover the details within historical photographs of Albert Einstein's brain [1]. The brain was sectioned after Einstein's death and samples have been studied by several researchers over the years, including Falk. The research was recently covered by the TV program NOVA ScienceNOW, which is being rebroadcast this week.
I wanted to point to the article by Falk and colleagues because it includes a brief discussion of the lunate sulcus -- one of the most persistently pernicious topics in paleoneurology.
The terminology for sulci of the human occipital lobe, in particular, has been influenced by an erroneous historical claim that human brains manifest a so-called lunate sulcus that is homologous to the Affenspalte (‘ape sulcus’) that forms the rostral boundary of the primary visual cortex [Brodmann area (BA) 17] on the lateral surface of the brain in apes and some monkeys (Smith, 1904, 1925). However, BA 17 of humans may, or may not, extend onto the external surface of the occipital lobe. When it does, its rostral border is located far posterior to the normal position for ape brains and is rarely bordered by a sulcus (Allen et al., 2006). Despite the fact that recent gross morphological and cytoarchitectural studies refute the assertion that humans have a lunate sulcus that is homologous with the Affenspalte (Allen et al., 2006; see Falk, 2012 for a discussion of the evolutionary implications), contemporary authors continue to use a variety of criteria to identify different sulci as so-called lunate sulci in humans (Duvernoy et al., 1999; Iaria and Petrides, 2007). The classical terminology used by Connolly (1950) for the occipital lobe is also grounded on the mistaken notion that humans have lunate sulci that are homologous to those of apes. For example, Connolly (1950) identifies a prelunate sulcus, which we identify with its modern name of the lateral occipital sulcus (Table 1). For these reasons, we do not recognize a lunate sulcus in Einstein’s brain.
The long-running argument over the possible location of the lunate sulcus in the endocast of the Taung fossil hominin was a heated debate for more than 20 years in paleoanthropology. For Falk, the end of the story is that the sulcal patterns in human and other primate brains in this region are not homologous -- making it problematic to recognize either in the fossil endocasts of early hominins. I'm sure it isn't over, but I find it inspiring to see the evolutionary record make an appearance in this consideration of the brain of a very famous scientist.
