The cerebellum and its contribution to complex tasks in higher primates: a comparative perspective.

Many aspects of the involvement of the cerebellum in motor control and cognition are still quite unclear or relatively unexplored. In particular, very little is known about the evolution of cerebellar contribution to complex behavior in higher primate species. In this paper, we provide an overview of existing and ongoing comparative studies of the role of the cerebellum in primate behavior.

Volumetric and lateralized differences in selected brain regions of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus).

The two species of Pan, bonobos and common chimpanzees, have been reported to have different social organization, cognitive and linguistic abilities and motor skill, despite their close biological relationship. Here, we examined whether bonobos and chimpanzee differ in selected brain regions that may map to these different social and cognitive abilities. Eight chimpanzees and eight bonobos matched on age, sex and rearing experiences were magnetic resonance images scanned and volumetric measures were obtained for the whole brain, cerebellum, striatum, motor-hand area, hippocampus, inferior frontal gyrus and planum temporale.

The chimpanzee brain shows human-like perisylvian asymmetries in white matter.

Modern neuroimaging technologies allow scientists to uncover interspecies differences and similarities in hemispheric asymmetries that may shed light on the origin of brain asymmetry and its functional correlates. We analyzed asymmetries in ratios of white to grey matter in the lateral aspect of the lobes of the brains of chimpanzees. We found marked leftward asymmetries for all lobar regions.

Handedness for tool use correlates with cerebellar asymmetries in chimpanzees (Pan troglodytes).

Recent studies have shown that great ape species possess patterns of macrostructural neocortical asymmetries that are similar to those found in humans. However, little is known about the asymmetry of subcortical structures in great apes. To address this lack of data, the authors assessed left-right asymmetry of the anterior and posterior aspects of cerebellum from MRI brain scans of 53 chimpanzees (Pan troglodytes).

Neuroanatomical correlates of handedness for tool use in chimpanzees (Pan troglodytes): implication for theories on the evolution of language.

It has been hypothesized that cognitive mechanisms underlying lateralized complex motor actions associated with tool use in chimpanzees may have set the stage for the evolution of left-hemisphere specialization for language and speech in humans. Here we report evidence that asymmetries in the homologues to Broca's and Wernicke's areas are associated with handedness for tool use in chimpanzees. These results suggest that the neural substrates of tool use may have served as a preadaptation for the evolution of language and speech in modern humans.

Handedness is associated with asymmetries in gyrification of the cerebral cortex of chimpanzees.

Gyrification of the cerebral cortex reflects complexity in cortical folding during development of the brain. In this paper, we evaluated whether chimpanzees show asymmetries in gyrification and if variation in gyrification asymmetries were associated with handedness. Magnetic resonance images were obtained in a sample of 76 chimpanzees, and gyrification measures were obtained from 10 equally spaced slices of the cortex.

The Association between handedness, brain asymmetries, and corpus callosum size in chimpanzees (Pan troglodytes).

It has been suggested from studies in human subjects that sex, handedness, and brain asymmetries influence variation in corpus callosum (CC) size and these differences reflect the degree of connectivity between homotopic regions of the left and right cerebral hemispheres. Here we report that handedness is associated with variation in the size of the CC in chimpanzees. We further report that variation in brain asymmetries in a cortical region homologous to Broca's area is associated with the size of the CC but differs for right- and left-handed individuals.

Gesture handedness predicts asymmetry in the chimpanzee inferior frontal gyrus.

Neuroanatomical asymmetries have been identified in chimpanzee frontal and temporal lobes including regions believed to be homologous to human Broca's and Wernicke's areas. This study examined whether or not neuroanatomical asymmetries in chimpanzees are associated with hand use during gestural communication. Analyses revealed that those chimpanzees that reliably employ their right hand for manual gestures have larger inferior frontal gyri in the left hemisphere than those apes that do not show consistent hand use for gestures.

Further evidence of an association between handedness and neuroanatomical asymmetries in the primary motor cortex of chimpanzees (Pan troglodytes).

The neurobiology of handedness is still poorly understood in nonhuman primates. Recently, an association between hand preference and precentral gyrus morphology in chimpanzees was reported. The aim of this study was to further evaluate the association between handedness and asymmetries in the precentral gyrus of chimpanzees (Pan troglodytes) and to evaluate the association between hand preference and brain asymmetry using a different approach to the classification of handedness in chimpanzees.

Chimpanzees are right-handed when recording bouts of hand use.

Whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. Previous research has shown that chimpanzees are right-handed when frequencies of hand use are recorded but some have questioned the validity of this approach. In this study, we evaluated handedness in 180 captive chimpanzees for a task measuring bimanual actions.

Individual and setting differences in the hand preferences of chimpanzees (Pan troglodytes): a critical analysis and some alternative explanations.

Several recent papers have been critical at a theoretical and empirical level of the evidence of population-level right-handedness in chimpanzees and other great apes. For example, Palmer (2002) has recently argued that the evidence of population-level handedness in chimpanzees is weak because there are sampling biases in the data. McGrew and Marchant (1997) argue that all the evidence of right-handedness in apes is from captive animals and therefore the observed phenomenon has little ecological validity.

Asymmetries in the hippocampus and amygdala of chimpanzees (Pan troglodytes).

Magnetic resonance imaging was used to measure the hippocampal and amygdalar volumes of 60 chimpanzees (Pan troglodytes). An asymmetry quotient (AQ) was then used to calculate the asymmetry for each of the structures. A one-sample t test indicated that there was a population-level right hemisphere asymmetry for the hippocampus.

Handedness in chimpanzees (Pan troglodytes) is associated with asymmetries of the primary motor cortex but not with homologous language areas.

The neurobiology of hand preferences in nonhuman primates is poorly understood. In this study, the authors report the first evidence of an association between hand preference and precentral gyrus-morphology in chimpanzees (Pan troglodytes). Hand preferences did not significantly correlate with other asymmetric brain regions associated with language functions in humans including the planum temporale and frontal operculum.

Further evidence for mirror-reversed laterality in lines of fish selected for leftward or rightward turning when facing a predator model.

In the teleost fish Girardinus falcatus eye preferences for inspecting a potential predator is highly heritable and this consented to select lines with opposed laterality. In previous studies individuals from a RD line (rightward turning when facing a dummy predator) and those from a LD line (leftward turning) were subjected to several other laterality tests (most of which, possibly all, were visually based). Since they obtained opposite scores in all tests, it was suggested that LD and RD fish have complete mirror-reversed organizations of the brain.

Population lateralisation and social behaviour: a study with 16 species of fish.

We investigated turning responses in 16 species of fish faced with a vertical-bar barrier through which a learned dummy predator was visible. Ten of these species showed a consistent lateral bias to turn preferentially to the right or to the left. Species belonging to the same family showed similar directions of lateral biases.

Are planum temporale and sylvian fissure asymmetries directly related? A MRI study in great apes.

In humans and great apes, both the planum temporale (PT-part of Wernicke's area) and the sylvian fissure (SF) in the left cerebral hemisphere have been consistently shown to be larger than the corresponding structures in the right hemisphere. The greater length of the SF in the left hemisphere is commonly thought to be a direct consequence of the larger expansion of the PT in the same hemisphere. However, there is a lack of studies that have attempted to directly assess the tenability of this hypothesis.

Grip morphology and hand use in chimpanzees (Pan troglodytes): evidence of a left hemisphere specialization in motor skill.

Three experiments on grip morphology and hand use were conducted in a sample of chimpanzees. In Experiment 1, grip morphology when grasping food items was recorded, and it was found that subjects who adopted a precision grip were more right-handed than chimpanzees using other grips. In Experiment 2, the effect of food type on grasping was assessed.

Lateralized reaching as dynamical symmetry breaking in the bushbaby (Otolemur garnettii): preliminary evidence.

Eight bushbabies were subjected to an extensive series of hand preference trials in which they were required to reach for a raisin from a rotating platform approaching from the right- or left-hand side of their visual field. Three principal types of behavior were observed. Several individuals known to be stable in hand preference continued to show a strong preference for a single hand.

Asymmetric Broca's area in great apes.

Brodmann's area 44 delineates part of Broca's area within the inferior frontal gyrus of the human brain and is a critical region for speech production, being larger in the left hemisphere than in the right - an asymmetry that has been correlated with language dominance. Here we show that there is a similar asymmetry in this area, also with left-hemisphere dominance, in three great ape species (Pan troglodytes, Pan paniscus and Gorilla gorilla). Our findings suggest that the neuroanatomical substrates for left-hemisphere dominance in speech production were evident at least five million years ago and are not unique to hominid evolution.

Interaction between lateralized systems: exploring the complexity of laterality.

To assess the extent of interaction between lateral biases in response systems at different levels of the neuraxis and detect the possible presence of different patterns of interaction related to population subgroups, we investigated laterality in hand reaching, whole-body turning and eye use in 20 bushbabies (Otolemur garnettii). Two subgroups were clearly identified: the STABLE group was composed of subjects, mainly females, that were consistent in hand preference and had correlation of hand/eye bias; the UNSTABLE group included subjects, mainly males, that showed instability in hand preference as a function of change in test conditions and had correlation of hand/turning bias. Results are interpreted to support the value of the study of interaction between lateral biases as a way of gaining a deeper understanding of the complexity of laterality.

First Results from Viper: Detection of Small-scale Anisotropy at 40 GHz.

Results of a search for small-scale anisotropy in the cosmic microwave background (CMB) are presented. Observations were made at the South Pole using the Viper telescope, with a 0&fdg;26 (FWHM) beam and a passband centered at 40 GHz. Anisotropy band-power measurements in bands spanning the range of l in which the first acoustic peak is expected (bands centered at l=108, 173, 237, 263, 422, and 589) are reported.

Origins and functions of laterality: interactions of motoric systems.

To evaluate lateral motoric bias in response systems at different levels of the neuraxis and assess the extent of interaction between these levels in the small-eared bushbaby (Otolemur garnettii), 27 animals were tested for lateral bias in hand use and whole-body turn bias in two postural conditions. Subjects retrieved mealworms quadrupedally by reaching downwards into glass jars and bipedally by reaching upwards to baited straws. Eye bias was assessed separately.

Pawedness and motor asymmetries in toads.

Pawedness was investigated in three species of toads, Bufo bufo , Bufo viridis , and Bufo marinus. Samples from natural populations were collected in two successive years and tested during attempts to remove a strip of paper stuck onto the snout ( Bufo bufo and Bufo viridis ) or during attempts to remove an elastic balloon wrapped around the head ( Bufo bufo ). A preferential right forelimb use at the population level was observed in Bufo bufo in both tests, whereas no clear pawedness was observed in Bufo viridis.