Snakes and their relationships with humans and other primates have attracted broad attention from multiple fields of study, but not, surprisingly, from neuroscience, despite the involvement of the visual system and strong behavioral and physiological evidence that humans and other primates can detect snakes faster than innocuous objects. Here, we report the existence of neurons in the primate medial and dorsolateral pulvinar that respond selectively to visual images of snakes. Compared with three other categories of stimuli (monkey faces, monkey hands, and geometrical shapes), snakes elicited the strongest, fastest responses, and the responses were not reduced by low spatial filtering. These findings integrate neuroscience with evolutionary biology, anthropology, psychology, herpetology, and primatology by identifying a neurobiological basis for primates' heightened visual sensitivity to snakes, and adding a crucial component to the growing evolutionary perspective that snakes have long shaped our primate lineage.evolution | Snake Detection Theory | visual responses | low-pass filtered images S nakes have long been of interest to us above and beyond the attention we give to other wild animals. The attributes of snakes and our relationships with them have been topics of discussion in fields as disparate as religion, philosophy, anthropology, psychology, primatology, and herpetology (1, 2). Ochre and eggshells dated to as early as 75,000 y ago and found with cross-hatched and ladder-shaped lines (3, 4) resemble the dorsal and ventral scale patterns of snakes. As the only natural objects with those characteristics, snakes may have been among the first models used in representational imagery created by modern humans. Our interest in snakes may have originated much further back in time; our primate lineage has had a long and complex evolutionary history with snakes as competitors, predators, and prey (1). The position of primates as prey of snakes has, in fact, been argued to have constituted strong selection favoring the evolution of the ability to detect snakes quickly as a means of avoiding them, beginning with the earliest primates (2, 5). Across primate species, ages, and (human) cultures, snakes are indeed detected visually more quickly than innocuous stimuli, even in cluttered scenes (6-11). Physiological responses reveal that humans are also able to detect snakes visually even before becoming consciously aware of them (12). Although the visual system must be involved in the preferential ability to detect snakes rapidly and preconsciously or automatically, the neurological basis for this ability has not yet been elucidated, perhaps because an evolutionary perspective is rarely incorporated in neuroscientific studies. Our study helps to fill this interdisciplinary gap by investigating the responses of neurons to snakes and other natural stimuli that may have acted as selective pressures on primates in the past.Here, we identify a mechanism for the visual system's involvement in rapid snake detection by measurin...

Natural products are excellent sources of lead compounds in the search for new medicaments for the treatment of diseases. The largest present underexplored source of such materials lies in tropical and subtropical regions of the world. In these areas, a long tradition of ethnobotanical medicine often exists and offers a rich and relatively untapped source for the discovery of new drugs from natural products. Vietnam, a tropical Southeast Asian country, also has a long history of traditional medicine systems. 1) However, systematic exploitation of these natural resources for their human health benefits has not been carried out to a significant degree.Gout is a common disease with a worldwide distribution. Hyperuricemia, which is associated with gout, results from the overproduction or underexcretion of uric acid and is greatly influenced by a high dietary intake of foods rich in nucleic acids, such as meats (especially organ meats), leguminous seeds, some types of seafood, and food yeasts. 2,3) During the last step of purine metabolism, xanthine oxidase (XO) catalyses the oxidation of xanthine and hypoxanthine into uric acid. 4) Uricosuric drugs which increase the urinary excretion of uric acid, or XO inhibitors which block the terminal step in uric acid biosynthesis, can lower the plasma uric acid concentration, and are generally employed for the treatment of gout.5) Allopurinol is a clinically used XO inhibitor in the treatment of gout, but this drug suffers from many side effects such as hepatitis, nephropathy, and allergic reactions.6) Thus, new alternatives with increased therapeutic activity and less side effects are desired. Moreover, superoxide anion radicals generated by XO are involved in various pathological states such as hepatitis, inflammation, ischemiareperfusion, carcinogenesis, and aging.2,7) Thus, the search for novel XO inhibitors would be beneficial not only to treat gout but also to combat various other diseases.To identify potential XO inhibitory agents from natural sources, we have tested 288 extracts prepared from 96 selected medicinal plants, which are used by the indigenous people in Vietnam for the treatment of gout or diseases associated with symptoms such as rheumatism, arthritis and inflammation. In addition, the active constituents of Chrysanthemum sinense, which showed the most potent XO inhibitory activity, have been determined. Chemicals Xanthine oxidase (EC 1.2.3.2) from bovine milk (10 units/ml) and xanthine were obtained from Sigma Chemical Co. (St. Louis, MO, U.S.A.). Allopurinol was purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Other reagents were of the highest grade available. MATERIALS AND METHODS Plant MaterialsPreparation of Samples Each medicinal plant (10-213 g) was cut into small pieces and extracted successively with MeOH (200-300 ml, reflux, 2 h, ϫ3), MeOH-H 2 O (1 : 1, 200-300 ml, reflux, 2 h, ϫ2), and water (200-300 ml, reflux, 2 h). The MeOH solution was evaporated under reduced pressure to give a MeOH extract, while MeOH-H 2 O (1 : 1) and w...

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The pulvinar nuclei appear to function as the subcortical visual pathway that bypasses the striate cortex, rapidly processing coarse facial information. We investigated responses from monkey pulvinar neurons during a delayed non-matching-to-sample task, in which monkeys were required to discriminate five categories of visual stimuli [photos of faces with different gaze directions, line drawings of faces, face-like patterns (three dark blobs on a bright oval), eye-like patterns and simple geometric patterns]. Of 401 neurons recorded, 165 neurons responded differentially to the visual stimuli. These visual responses were suppressed by scrambling the images. Although these neurons exhibited a broad response latency distribution, face-like patterns elicited responses with the shortest latencies (approximately 50 ms). Multidimensional scaling analysis indicated that the pulvinar neurons could specifically encode face-like patterns during the first 50-ms period after stimulus onset and classify the stimuli into one of the five different categories during the next 50-ms period. The amount of stimulus information conveyed by the pulvinar neurons and the number of stimulus-differentiating neurons were consistently higher during the second 50-ms period than during the first 50-ms period. These results suggest that responsiveness to face-like patterns during the first 50-ms period might be attributed to ascending inputs from the superior colliculus or the retina, while responsiveness to the five different stimulus categories during the second 50-ms period might be mediated by descending inputs from cortical regions. These findings provide neurophysiological evidence for pulvinar involvement in social cognition and, specifically, rapid coarse facial information processing.

The superficial layers of the superior colliculus (sSC) appear to function as a subcortical visual pathway that bypasses the striate cortex for the rapid processing of coarse facial information. We investigated the responses of neurons in the monkey sSC during a delayed non-matching-to-sample (DNMS) task in which monkeys were required to discriminate among five categories of visual stimuli [photos of faces with different gaze directions, line drawings of faces, face-like patterns (three dark blobs on a bright oval), eye-like patterns, and simple geometric patterns]. Of the 605 sSC neurons recorded, 216 neurons responded to the visual stimuli. Among the stimuli, face-like patterns elicited responses with the shortest latencies. Low-pass filtering of the images did not influence the responses. However, scrambling of the images increased the responses in the late phase, and this was consistent with a feedback influence from upstream areas. A multidimensional scaling (MDS) analysis of the population data indicated that the sSC neurons could separately encode face-like patterns during the first 25-ms period after stimulus onset, and stimulus categorization developed in the next three 25-ms periods. The amount of stimulus information conveyed by the sSC neurons and the number of stimulus-differentiating neurons were consistently higher during the 2nd to 4th 25-ms periods than during the first 25-ms period. These results suggested that population activity of the sSC neurons preferentially filtered face-like patterns with short latencies to allow for the rapid processing of coarse facial information and developed categorization of the stimuli in later phases through feedback from upstream areas.