Early hominid brain evolution: a new look at old endocasts

Early hominid brain morphology is reassessed from endocasts of Australopithecus africanus and three species of Paranthropus, and new endocast reconstructions and cranial capacities are reported for four key specimens from the Paranthropus clade. The brain morphology of Australopithecus africanus appears more human like than that of Paranthropus in terms of overall frontal and temporal lobe shape. These new data do not support the proposal that increased encephalization is a shared feature between Paranthropus and early Homo. Our findings are consistent with the hypothesis that Australopithecus africanus could have been ancestral to Homo, and have implications for assessing the tempo and mode of early hominid neurological and cognitive evolution.

Cranial capacity and performance on delay-response task correlated with principal sulcus length in monkeys

During the process of evolution, a selective advantage may have been gained by organisms that had the ability to utilize mentally stored information of a stimulus rather than the stimulus itself. The ability to temporarily store and mentally operate on stimulus information is often termed "working memory." Within the neocortex of primates, the functional anatomic subdivision surrounding the principal (rectus) sulcus plays an important role in modulating the performance of delay-response tasks in monkeys (representing working memory). However, it appears that no study has investigated the direct relationship between the length of the principal sulcus and performance on a delay-response task. Therefore, this paper investigates the relationships between principal sulcus length and performance on delay-response tasks. However, to control for the effect of overall brain size on this relationship, cranial capacity is analyzed with both principal sulcus length and delay-response performance. Results support a consistent and significant correlation between principal sulcus length and performance on delayed-response tasks in a variety of Old World and New World monkeys. Principal sulcus length is also significantly correlated with cranial capacity; however, cranial capacity is not significantly correlated with performance on delayed-response tasks. The results of this investigation provide a method for analyzing cranial capacity and working-memory abilities in select primates based on principal sulcus length, and may prove useful for interpreting endocasts in the primate fossil record.

Localization of dopamine receptor subtypes occupied by intra-accumbens antagonists that reverse cocaine-induced locomotion

The purpose of this study was to examine whether blockade of either dopamine D1-like or D2-like receptors by selective antagonist administration into the nucleus accumbens (NAc) is sufficient to reverse cocaine-induced locomotion, and to develop a new technique that enables the population of receptors occupied by the antagonists to be quantified. Locomotor activity was assessed in rats that had received bilateral intra-accumbens injections of the D1-selective antagonist SCH-23390 (0-3.0 micrograms/0.5 microliters/side) or the D2/D3-selective antagonist sulpiride (0-1.0 micrograms/0.5 microliters/side), followed 15 min later by injections of saline or cocaine (15 mg/kg, i.p.). To assess receptor occupancy by the antagonists, 105 min prior to sacrifice the rats received intra-accumbens injections of the antagonist, followed 15 min later by an injection of the non-selective irreversible antagonist, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ; 10 mg/kg, i.p.). Receptors were labeled with [3H]SCH-23390 or [3H]sulpiride in sections containing the NAc, and the autoradiograms allowed quantitation of receptors occupied (i.e. protected from EEDQ) by the antagonist given in vivo. Only a dose of 3 micrograms/side SCH-23390 reversed cocaine-induced locomotion, whereas a dose of 0.5 microgram/side did not alter cocaine-induced locomotion despite occupying the same amount of [3H]SCH-23390 binding sites in the NAc. Intermediate doses of 0.1 and 0.3 microgram/side sulpiride reversed cocaine-induced locomotion, and also occupied the greatest number of [3H]sulpiride binding sites in the NAc. The results suggest that blockade of D2-like, but not D1-like, receptors in the NAc is sufficient to reverse cocaine-induced locomotion, and also demonstrate the importance of quantifying receptors occupied by drugs administered intracranially.