Abstract: The minicolumn is generally considered an elementary unit of the neocortex in all mammalian brains. This essential building block has been affected by changes in the circuitry of the cortex during evolution. Researchers believe that enlargement of the cortical surface occurs through the addition of minicolumns rather than of single neurons. Therefore, minicolumns integrate cortical encephalization with organization. Despite these insights, few studies have analyzed the morphometry of the minicolumn to detect subtle but important differences among the brains of diverse mammals. The notion that minicolumns are essentially unchanged across species is challenged by strong evidence to the contrary. Because they are subject to species-specific variation, they can be used as a way to study evolutionary changes. Unfortunately, comparative studies are marred by a lack of standardized techniques, tissue preparation, cortical regions, or anatomical feature studied. However, recent advances in methodology enable standardized, quantified comparisons of minicolumn morphology.

Abstract: The behavior of reproductive female ants distinctly changes during the transition from virgin to mature, egg-laying queen. A winged female ant flies only once during her lifetime when she engages in t

Abstract: Previous reports have suggested that the sparsely distributed hairs found on the entire postcranial body of sirenians are all sinus type tactile hairs. This would represent a unique arrangement because no other mammal has been reported to possess tactile hairs except on restricted regions of the body, primarily the face. In order to investigate this issue further, hair counts were made systematically in three Florida manatees (Trichechus manatus latirostris) , and hair follicle microanatomy was studied in 110 specimens gathered from 9 animals. We found that the postcranial body possesses approximately 1500 hairs per side, and hair density decreases from dorsal to ventral. External hair length ranged from 2–9 mm, and most hairs were separated from their nearest neighbor by 20–40 mm, resulting in an independent domain of movement for each hair. All hairs exhibited the anatomical characteristics of follicle-sinus complexes typical of tactile hairs, including a dense connective tissue capsule containing an elongated circumferential blood sinus and innervation by 20–50 axons which ascend the mesenchymal sheath. We conclude that this represents a unique distributed underwater tactile system capable of conveying detailed and significant external information concerning approaching animals, water currents and possibly the presence of large stationary features of the environment. Such a system would be analogous to the lateral line in fish, and would be particularly useful in the turbid habitat frequented by Florida manatees.

Abstract: Neurochemical, hodological and functional criteria suggest that the nucleus taeniae and parts of the adjacent archistriatum represent the avian homologue of parts of the mammalian amygdaloid complex. It has been proposed in particular that the nucleus taeniae is the homologue of the mammalian medial amygdala. In male quail, relatively large lesions to the posterior/medial archistriatum selectively decrease the expression of appetitive sexual behavior in a manner reminiscent of similar manipulations involving the medial amygdala in mammals. We investigated the effects of discrete lesions restricted to nucleus taeniae and of lesions to an adjacent part of the archistriatum (pars intermedium ventralis, AIv) on the expression of appetitive (ASB) and consummatory (CSB) aspects of male sexual behavior. ASB was measured by a learned social proximity response (after copulation a male quail stands in front of a window providing visual access to a female) and by the frequency of rhythmic cloacal sphincter movements. CSB was assessed by the frequency of mount attempts (MA) and cloacal contact movements (CCM). Lesions confined to nucleus taeniae and to AIv did not influence the acquisition or the maintenance of the two responses indicative of ASB. In contrast, lesions of nucleus taeniae significantly increased the occurrence frequencies of MA and CCM when administered before the beginning of behavior testing and increased the frequency of MA only when performed on sexually experienced subjects. No effect of AIv lesions could be detected. The discrepancy between these results and previous experiments in quail might reflect procedural differences, but more probably differences in locations of the lesions that were restricted in the current study to the anterior part of taeniae. Those in the Thompson study were in the posterior part of this nucleus. These findings indicate that there is a larger degree of functional heterogeneity in the nucleus taeniae than previously thought. The effects of taeniae lesions suggest that this nucleus, similar to the medial amygdala in mammals, might be implicated in the control of sexual satiety.

Abstract: Water movements, of both abiotic and biotic origin, provide a wealth of information of direct relevance to the guidance of prey capture behavior. To gather hydrodynamic information, fish have sensors

Abstract: Early efforts to reconstruct the course of the evolution of the human brain relied on comparing the brains of a few related mammals with brains at successively higher levels of complexity. This Clark or ladder of levels approach is now seen as having limited usefulness in that species are not easily assigned to levels, and extant mammals are now recognized as mosaics of primitive and derived features. In addition, direction of change does not necessarily proceed from simple to complex, small to large, or diffuse to differentiated. A modern cladistic approach reconstructs the brains of ancestors by identifying brain characters within and across phylogenetic groups (clades), and uses parsimony or likelihood to infer direction of change and distinguish ancestral features from independently evolved convergences. Unfortunately, an idealized cladistic approach is often difficult to realize because characters may be hard to identify and validate, key species may be unavailable for study, and broadly based comparative studies can be costly, poorly funded, and labor intensive. Thus, many investigators pursue a truncated approach that is superficially Clark-like but conceptually cladistic. A truncated approach that relies on the extensive study of a few species may compensate for weaknesses by including niche-matched species that offer the opportunity to estimate the likelihood of similar brain features evolving as convergent adaptations. Because inferences about the brains of the primate ancestor are often made from the brains of tree shrews, we compare the brains of squirrel-like tree shrews with the brains of diurnal squirrels, and suggest that many of the primate-like features of the visual system of tree shrews arose independently of those in primates.

Abstract: Divergence and convergence are two evolutionary processes by which organisms become adapted to their environments. With the advent of molecular biological techniques it is possible to ask if these processes are observed at the molecular level. There are many examples of molecular divergence in which molecular sequence or function change over evolutionary time. There are fewer reports of convergent evolution on the molecular level, and these claims are sometimes controversial. In this paper I discuss the types of convergent molecular evolution, describe the criteria for accepting or rejecting convergence, and give some examples relevant to neurobiology where convergence has been claimed. These include convergent evolution of opsins, gap junction proteins, neurotransmitter receptors, ion channels, and venoms directed against ion channels.

Abstract: Black ghost knifefish (Apteronotus albifrons) are nocturnal, weakly electric fish that feed on insect larvae and small crustaceans in the freshwater rivers of South America. In the absence of visual cues, prey detection and localization in this species is likely to rely on weak electrosensory and mechanosensory cues generated by the prey. In this paper, a modeling approach is used to estimate contributions to prey capture behavior from three octavolateralis modalities: the high- (tuberous) and low- (ampullary) frequency components of the electric sense and the high-frequency (canal neuromast) component of the lateral line mechanosensory system. For each of these modalities, the physical stimulus generated by the prey is approximated using a simple dipole model. Model parameters are constrained using previously published data as well as new empirical data on the electrical impedance characteristics of Daphnia magna. Models of electrosensory and mechanosensory stimuli are combined with actual prey strike trajectories from infrared video recordings to reconstruct spatial images of the prey along the sensory surface of the fish during the behavior. Modeling results suggest that all three modalities might contribute and that the relative contributions may change as a function of environmental conditions (e.g., water conductivity) and as a function of time over the course of the prey capture event.

Abstract: Studies of sleep in cetaceans (whales, dolphins, and porpoises), substantiated by electrophysiological data, are rare with the great majority of observations having been made by one group from Russia.

Abstract: During the past 24 years, I have used a modeling technique (M/R procedure) to train Grey parrots to use an allospecific code (English speech) referentially; I then use the code to test their cognitive abilities. The oldest bird, Alex, labels more than 50 different objects, 7 colors, 5 shapes, quantities to 6, 3 categories (color, shape, material) and uses ‘no’, ‘come here’, wanna go X’ and ‘want Y’ (X and Y are appropriate location or item labels). He combines labels to identify, request, comment upon or refuse more than 100 items and to alter his environment. He processes queries to judge category, relative size, quantity, presence or absence of similarity/difference in attributes, and show label comprehension. He semantically separates labeling from requesting. He thus exhibits capacities once presumed limited to humans or nonhuman primates. Studies on this and other Greys show that parrots given training that lacks some aspect of input present in M/R protocols (reference, functionality, social interaction) fail to acquire referential English speech. Examining how input affects the extent to which parrots acquire an allospecific code may elucidate mechanisms of other forms of exceptional learning: learning unlikely in the normal course of development but that can occur under certain conditions.

Abstract: Over the past 20 years, cladistic analyses have revolutionized our understanding of brain evolution by demonstrating that many structures, some of which had previously been assumed to be homologous, have evolved many times independently. These and other studies demonstrate that evolutionary convergence in brain anatomy and function is widespread. Although there are relatively few neuroethological studies in which brain and behavior have be studied within an evolutionary framework, three relatively well studied cases are reviewed here: electric communication among gymnotiform and mormyriform fishes, prey capture among frogs, and sound localization among owls. These three examples reveal similar patterns of brain evolution. First, it is clear that novel abilities have evolved many times independently in taxa whose common ancestors lack these abilities. Second, it is apparent that small changes in neural pathways can lead to dramatic changes in an organism's abilities. Brain evolution at this small scale is quite common. The behavioral importance of small scale changes on one hand, and the pervasiveness of convergent evolution on the other, have several implications for understanding brain evolution. First, similar abilities may be conferred by convergent rather than homologous circuits, even among closely related species. Furthermore, closely related species may use the same information in different ways, or they may use different means to obtain the same information. One reason that convergence is so common in the biological world may be that the evolutionary appearance of novel functions is associated with constraints, for example in the algorithms used for a given neural computation. Convergence in functional organization may thus reveal basic design features of neural circuits in species that possess unique evolutionary histories but use similar algorithms to solve basic computational problems.

Abstract: An evolutionarily conserved feature of neural systems is that they can be modified by neuromodulators. These modulatory chemical signals include the biogenic amines, octopamine (OA), serotonin (5-HT) and dopamine (DA). Such modulation effectively broadens the operational range in which specific neural circuits can function adaptively. This report discusses how these amines are themselves modulated; for example, by the steroid hormone 20-hydroxyecdysone (20-E) or by the addition of a second biogenic amine. Such second-order neuromodulation, termed metamodulation, is discussed in the context of two well-studied invertebrate systems: the tobacco hornworm moth Manduca sexta, a model of neurodevelopment and plasticity, and the medicinal leech Hirudo medicinalis, a long-favored preparation used to study neural circuits at the level of identified neurons. A portion of this article reviews our previous research of M. sexta that shows that the ‘preadult’ rise in 20-E is both necessary and sufficient for the increased levels of octopamine observed in the adult. Such elevated levels likely play an important role in the production and modulation of adult behaviors. The somatic growth of median octopaminergic neurons and the late expression of OA-immunoreactivity by novel lateral neurons are also demonstrated to be dependent on 20-E. New immunocytochemical results of stained dopaminergic neurons in the larval and adult moth brain are provided as well, and the potential influence of 20-E on the developmental expression of this neuromodulator is presented. Turning attention to the leech, data indicate that the actions of OA are dramatically altered when 5-HT is combined with OA in the bath surrounding the isolated nervous system. Although either OA or 5-HT alone induces fictive swimming behavior, a cocktail of these two amines strongly inhibits the generation of swimming. Subsequent removal of such a mixture induces nearly continuous swimming and constitutes the best swim-inducing stimulus encountered to date. To understand better how these nonadditive effects are achieved, new results are discussed that indicate that the leech brain is the target of metamodulation by the two amines. Both the arthropod and annelid systems presented here highlight the multiple levels of metamodulation that can exist in nervous systems, and the diverse ways that a modulator’s actions can become altered over short or long time periods.

Abstract: Numerous animals across disparate taxa must identify and locate complex acoustic signals imbedded in multiple overlapping signals and ambient noise. A requirement of this task is the ability to group sounds into auditory streams in which sounds are perceived as emanating from the same source. Although numerous studies over the past 50 years have examined aspects of auditory grouping in humans, surprisingly few assays have demonstrated auditory stream formation or the assignment of multicomponent signals to a single source in non-human animals. In our study, we present evidence for auditory grouping in female tungara frogs. In contrast to humans, in which auditory grouping may be facilitated by the cues produced when sounds arrive from the same location, we show that spatial cues play a limited role in grouping, as females group discrete components of the species' complex call over wide angular separations. Furthermore, we show that once grouped the separate call components are weighted differently in recognizing and locating the call, so called 'what' and 'where' decisions, respectively.

Abstract: Previously we described patterns of connections that support the concept of V3 in small New World marmoset monkeys, three species of larger New World monkeys, and two species of Old World macaque monk

Abstract: The present study employs choline acetyltransferase (ChAT) immunohistochemistry to identify the cholinergic neuronal population in the central nervous system of the monotremes. Two of the three extant species of monotreme were studied: the platypus (Ornithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus). The distribution of cholinergic cells in the brain of these two species was virtually identical. Distinct groups of cholinergic cells were observed in the striatum, basal forebrain, habenula, pontomesencephalon, cranial nerve motor nuclei, and spinal cord. In contrast to other tetrapods studied with this technique, we failed to find evidence for cholinergic cells in the hypothalamus, the parabigeminal nucleus (or nucleus isthmus), or the cerebral cortex. The lack of hypothalamic cholinergic neurons creates a hiatus in the continuous antero-posterior aggregation of cholinergic neurons seen in other tetrapods. This hiatus might be functionally related to the phenomenology of monotreme sleep and to the ontogeny of sleep in mammals, as juvenile placental mammals exhibit a similar combination of sleep elements to that found in adult monotremes.

Abstract: The distribution and cellular morphology of serotonergic neurons in the brain of two species of monotremes are described. Three clusters of serotonergic neurons were found: a hypothalamic cluster, a cluster in the rostral brainstem and a cluster in the caudal brainstem. Those in the hypothalamus consisted of two groups, the periventricular hypothalamic organ and the infundibular recess, that were intimately associated with the ependymal wall of the third ventricle. Within the rostral brainstem cluster, three distinct divisions were found: the dorsal raphe nucleus (with four subdivisions), the median raphe nucleus and the cells of the supralemniscal region. The dorsal raphe was within and adjacent to the periaqueductal gray matter, the median raphe was associated with the midline ventral to the dorsal raphe, and the cells of the supralemniscal region were in the tegmentum lateral to the median raphe and ventral to the dorsal raphe. The caudal cluster consisted of three divisions: the raphe obscurus nucleus, the raphe pallidus nucleus and the raphe magnus nucleus. The raphe obscurus nucleus was associated with the dorsal midline at the caudal-most part of the medulla oblongata. The raphe pallidus nucleus was found at the ventral midline of the medulla around the inferior olive. Raphe magnus was associated with the midline of the medulla and was found rostral to both the raphe obscurus and raphe pallidus. The results of our study are compared in an evolutionary context with those reported for other mammals and reptiles.

Abstract: Neuromodulation provides a means of changing the excitability of neurons or the effect of synapses, and so extends the performance range of neural circuits. Metamodulation occurs when the neuromodulat

Abstract: The stage of cerebellar development at birth was assessed in 23 species of placental mammals. Serial histological sections were examined and five stages in the differentiation of the cerebellar cortic

Abstract: Efferent fiber connections of the corpus and valvula cerebelli in the goldfish, Carassius auratus, were studied using an anterograde neural fiber tracing technique. Efferent targets of the corpus cerebelli are the posterior parvocellular preoptic nucleus, the ventromedial and ventrolateral thalamic nucleus, dorsal posterior thalamic nucleus, periventricular nucleus of posterior tuberculum, dorsal periventricular pretectal nucleus, inferior lobe, optic tectum, torus semicircularis, nucleus of the medial longitudinal fascicle, nucleus ruber, dorsal tegmental nucleus, nucleus lateralis valvulae, reticular formation, torus longitudinalis, and the medial and lateral lobe of the valvula cerebelli. Projections to the posterior parvocellular preoptic nucleus and the periventricular nucleus of posterior tuberculum are not reported in previous studies. Efferent targets of the medial lobe of the valvula cerebelli are similar to that of the corpus cerebelli except for lacking a projection to the inferior lobe and torus longitudinalis, but showing one to the corpus cerebelli. On the other hand, the lateral lobe of the valvula cerebelli projects only to the dorsal zone of the periventricular hypothalamus, the diffuse nucleus of the inferior lobe, corpus mamillare, vagal lobe and the corpus cerebelli. There are topographical projections from the lateral valvula to the inferior lobe. These results suggest that the function of the corpus and medial lobe of the valvula cerebelli include not only motor control but also functions similar to the mammalian higher cerebellum. This study also suggests that there are obvious functional divisions between the medial and lateral lobes of the valvula cerebelli.

Abstract: The ability of neuropeptides to modulate neural circuit activity is well established, but little is known regarding how the actions of neurally-released peptides are regulated. This issue is being stu

Abstract: The present study describes the distribution and cellular morphology of catecholaminergic neurons in the CNS of two species of monotreme, the platypus (Ornithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus) Tyrosine hydroxylase immunohistochemistry was used to visualize these neurons The standard A1–A17, C1–C3 nomenclature was used for expediency, but the neuroanatomical names of the various nuclei have also been given Monotremes exhibit catecholaminergic neurons in the diencephalon (A11, A12, A13, A14, A15), midbrain (A8, A9, A10), rostral rhombencephalon (A5, A6, A7), and medulla (A1, A2, C1, C2) The subdivisions of these neurons are in general agreement with those of other mammals, and indeed other amniotes Apart from minor differences, those being a lack of A4, A3, and C3 groups, the catecholaminergic system of monotremes is very similar to that of other mammals Catecholaminergic neurons outside these nuclei, such as those reported for other mammals, were not numerous with occasional cells observed in the striatum It seems unlikely that differences in the sleep phenomenology of monotremes, as compared to other mammals, can be explained by these differences The similarity of this system across mammalian and amniote species underlines the evolutionary conservatism of the catecholaminergic system

Abstract: Adult stingrays use their ampullary electroreceptors to detect prey and locate mates, but the response properties and function of their electrosensory system in the pre-adult stages are unknown. We examined the response properties of Atlantic stingray (Dasyatis sabina) electrosensory primary afferent neurons through ontogeny to determine whether encoding of electrosensory information changes with age, and how it relates to the ontogenetic encoding of biologically relevant electric stimuli. We show that during development electrosensory primary afferents increase resting discharge regularity, show an upward shift in best frequency (BF), an increase in neural sensitivity, and a decrease in bandpass. These ontogenetic changes in the response properties of the stingray electrosense are consistent with sensory adaptations to enhance the avoidance of large predators as young, and increase the location of prey and mates as adults.

Abstract: The claustrum, which comprises the claustrum proper and the endopiriform nucleus, is generally thought to be present in all mammals. Some previous reports of its possible absence in monotremes have appeared in the literature, but the question of its presence or absence in this clade has not been formally addressed. Whether monotremes have a claustrum is of some importance for formulating and evaluating hypotheses relating to the evolution of the structures in the lateral sector of the pallium across amniotes. Archival sets of sections through the brains of the platypus and the short-beaked echidna were examined and included material stained for seven different histochemical and immunohistochemical protocols. No cytoarchitectonically distinct claustrum could be identified in this material for either monotreme. We thus conclude that if monotremes have any cell population that is homolgous to the claustrum of therian mammals, it is entirely cryptic. A claustrum might have been present in ancestral mammals and lost in the monotreme clade, or it might have been gained at the origin of therian mammals. Nonetheless, its absence as a cytoarchitectonically discrete and identifiable structure in monotremes fails to support homology of the claustrum of therian mammals with any single part of the sauropsid pallium.

Abstract: Convergence is a pervasive evolutionary process, affecting many aspects of phenotype and even genotype. Relatively little is known about convergence in developmental processes, however, nor about the degree to which convergence in development underlies convergence in anatomy. A switch in the ecology of sea urchins from feeding to nonfeeding larvae illustrates how convergence in development can be associated with convergence in anatomy. Comparisons to more distantly related taxa, however, suggest that this association may be limited to relatively close phylogenetic comparisons. Similarities in gene expression during development provide another window into the association between convergence in developmental processes and convergence in anatomy. Several well-studied transcription factors exhibit likely cases of convergent gene expression in distantly related animal phyla. Convergence in regulatory gene expression domains is probably more common than generally acknowledged, and can arise for several different reasons.

Abstract: We investigated the spectral and morphological features of the photoreceptors of five atherinomorph teleosts, representing two different orders, and with different life styles and habitats, the Beloniformes and Atheriniformes The retinae of Belone belone (Belonidae), Dermogenys pusillus (Hemiramphidae), Atherina boyeri (Atherinidae), Marosatherina ladigesi (Telmatherinidae), and Melanotaenia maccullochi (Melanotaeniidae) were examined by light and electron microscopy and microspectrophotometry In addition to rods, five morphologically different cone types were identified: short, intermediary and long single cones, and double cones which are arranged in distinct specific mosaics Sporadically, triple cones were also found Double cones were longer-wave-sensitive, but no general correlation between single cone morphology and spectral sensitivity could be demonstrated The rods had λmax close to 506–509 nm The λmax of cone visual pigments ranged from about 368 nm to 578 nm Ultraviolet-sensitive single cones were present in the three freshwater species, M ladigesi, M maccullochi and D pusillus and three spectrally distinct short-wave-sensitive single cone classes were identified in M maccullochi In M ladigesi, spectral sensitivity varied among individuals due to varying rhodopsin/porphyropsin mixtures In D pusillus and M maccullochi polymorphism of the longer-wave cone pigments might occur These findings are discussed with respect to phylogeny, photic habitat, behavior and feeding habits

Abstract: The organization of nitrergic systems in the brains of anuran and urodele amphibians was recently studied and significant differences were noted between both amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study we have investigated the distribution of neuronal elements that express nitric oxide synthase (NOS) in the brain of the gymnophionan amphibian Dermophis mexicanus by means of immunohistochemistry with specific antibodies against NOS and enzyme histochemistry for NADPH-diaphorase. Both techniques yielded identical results and were equally suitable to demonstrate the nitrergic system. In addition, they were useful tools in the identification of cell groups and brain structures, otherwise indistinct in the brains of caecilians. The distribution of nitrergic structures observed in Dermophis conforms to the overall amphibian pattern but numerous distinct peculiarities were also noted. These included a dense innervation of the olfactory bulbs but a lack of reactivity in olfactory and vomeronasal fibers and glomeruli. A large population of nitrergic cells in the striatum and the presence of thalamic neurons, as well as the specific distribution of nitrergic cells in the isthmic region, are some of the differential features in the gymnophionan brain. Given the variability among species in the same class of vertebrates any discussion including amphibians should also include evidence for gymnophionans.

Abstract: In the New World monkey Saguinus fuscicollis, the anterograde projections of the motorcortical tongue area were studied. Three animals were analyzed. In two, biotin dextran amine was used as tracer; in the third, Phaseolus vulgaris leucoagglutinin was used. Identification of the tongue area was carried out by electrical brain stimulation. Intracortical projections were found into the neighboring primary motor cortex, ventral premotor cortex, frontoopercular cortex, and primary and secondary somatosensory cortex. Projections also ended in the ventrolateral prefrontal cortex, orbital cortex, supplementary motor area, anterior cingulate cortex and agranular as well as granular insula. In addition, weaker labeling was found in the inferior and dorsal parietal cortex, and perirhinal and inferotemporal cortex. Subcortically, there was a heavy projection into the ventral putamen, a moderate projection into the caudate nucleus and claustrum, and a weak projection into the anterior, central and lateral amygdala. In the thalamus, terminal labeling was found in the nuclei ventralis posterior medialis, ventralis lateralis, reticularis, centralis lateralis, medialis dorsalis, pulvinaris oralis, centrum medianum, reuniens and suprageniculatus in an order of intensity. Subthalamically, weak projections could be traced into the zona incerta and lateral hypothalamus. In the midbrain, labeling was found in the deep layers of the colliculus superior, area praetectalis, dorsal reticular formation and, very sparsely, in the periaqueductal gray. In the lower brainstem, fibers ended in the griseum pontis, medial and lateral parabrachial nuclei, lateral pontine and medullary reticular formation, paramedian and dorsal reticular nuclei, solitary tract nucleus and principal as well as spinal trigeminal nuclei. No terminals were found in the hypoglossal nucleus itself; there were, however, terminals in the immediately bordering reticular formation.

Abstract: This study examined how weakly electric fish, Gnathonemus petersii , integrate multiple sensory modalities (passive and active electrosenses, and vision) to maintain proximity to tub

Abstract: We present the results of 5 experiments that assessed 7 chimpanzees' understanding of the visual experiences of others. The research was conducted when the animals were adolescents (7-8 years of age) and adults (12 years of age). The experiments examined their ability to recognize the equivalence between visual and tactile modes of gaining the attention of others (Exp. 1), their understanding that the vision of others can be impeded by opaque barriers (Exps. 2 and 5), and their ability to distinguish between postural cues which are and are not specifically relevant to visual attention (Exps. 3 and 4). The results suggest that although chimpanzees are excellent at exploiting the observable contingencies that exist between the facial and bodily postures of other agents on the one hand, and events in the world on the other, these animals may not construe others as possessing psychological states related to 'seeing' or 'attention.' Humans and chimpanzees share homologous suites of psychological systems that detect and process information about both the static and dynamic aspects of social life, but humans alone may possess systems which interpret behavior in terms of abstract, unobservable mental states such as seeing and attention.