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Innate visual recognition E • Wolf decoy for geese (plenty in New England). • Why are these decoys efficient? • Geese do not have pictures to teach their young ones what animals to avoid… • … and so they must be born with images of predators engraved in their brain • Why are we surprised to observe innate predator recognition in visual domain? • For us innate predator recognition in the olfactory domain is much more intuitive. • Rats are born knowing the smell of cats. • Even humans are born with innate aversion to certain smells (such as smell of rotten eggs). Frogs • Frogs can recognize prey stimuli—worm-like objects—immediately after metamorphosis. (Although the accuracy of this recognition improves during ontogeny) • Lesion studies: bilateral ablation of both telencephalic hemispheres and removal of the dorsal thalamus Frogs readily responded to moving visual stimuli with prey orienting and snapping. • Lesions to the optic tectum (superior colliculus homologue) cause a total loss of responses to moving predator and prey objects. • In amphibian species, there are no telencephalic components that correspond to the visual cortex of mammalian species. • Conclusion: optic tectum includes all the neurons frogs need for visual recognition of predators and prey. Birds • Naive turkey chicks respond with escape behaviors to the overhead presentation of moving birdlike silhouettes. • Newly hatched chicks will peck at small objects shortly after birth and show definite preferences for certain types, colors and shapes of objects, even when these objects produce no reward. • Complete bilateral hemispherectomy performed in early life spares many behaviors that require stimulus discrimination, such as pecking at food objects, flying and cleaning feathers with beak Birds • Right after hatching chicks have the innate predisposition to approach stimuli that resemble their own species, both in their shape and color, and in the way they move. • Telencephalic ablation does not change preference for their own species. • The process of imprinting involves the learned recognition of a particular stimulus object, which becomes ‘mother’ for the chicks. • This imprinting is stored in telencephalon. Telencephalic ablation erases the imprinted memory. • Conclusion: same pattern as in frogs, chicks are born with neurons (in optic lobe = tectum) necessary for visual recognition of predators and food objects. Telencephalon is only necessary for memory. Rats • Naïve rats (laboratory born and raised) exposed to a cat respond with freezing behavior, and wild running and jumping. • Complete bilateral lesion of visual cortex same behavior. • Rodents without visual cortex pursue objects that move in a naturalistic fashion. As in the case of prey recognition in frogs, the precise shape of the stimulus object is not overly important, and recognition is primarily based on the characteristics of the movement of the object. • Conclusion: As in frogs and birds, recognition of predator and prey can be mediated primarily by optic tectum (superior colliculus). Primates • Snakes are oldest predators of monkeys. • The infant monkeys raised in isolation respond to the pictures of threatening monkeys with alarm vocalizations. • Wild-reared adult monkeys are afraid of both live snakes and snake models. Monkeys respond by moving to the back of the cage, jumping in the cage, etc. • Laboratory-reared adult monkeys react to the snakes with much milder avoidance responses. For example, of the juveniles that had been exposed to snakes as infants, six out of seven emitted alarm calls, while only one out of seven inexperienced subjects emitted an alarm call. • But no monkeys approached the snake and almost all of them oriented to the snake. Vervet monkey • Vervet monkey select correct calls for four classes of predators (a leopard, an eagle, a snake, a baboon). • A young vervet can mistakenly produce the raptor call to hawks (which resemble the true predator), produce the snake call to inappropriate snakes, and the leopard call to inappropriate ground animals. • It corrects these errors, learning to confine the call to the correct member of each category, and to respond more quickly. • However, even when the vervet produces its first calls, it does not make between-category errors, for example, issue the snake call to a bird, and so on. • That means they have innate representation of these classes in their brain. Humans • Human neonates at only 9 minutes from birth track a slowly moving schematic face stimulus with their head and eyes significantly further than they follow scrambled faces or blank stimuli. • As in frogs, birds, and monkeys, mediated by superior colliculi. • The tendency to orient to face-like stimuli continues into the second month, and thereafter decays to be replaced by learned recognition of individual faces, starting at approximately 3 months of age. • The learned response is mediated by the cortex. Conclusions: Innate visual recognition • Almost all vertebrates are capable of recognizing the classes of biologically relevant stimuli (prey vs. predator) at or shortly after birth. • In some phylogenetically ancient species (frogs) visual object recognition even in adulthood is exclusively innate. • In rodent species the innate sensory recognition systems function throughout ontogeny. In adulthood it is acting in parallel with the cortical recognition systems. • In primates the structures involved in innate stimulus recognition are essentially the same as those in rodents, but innate recognition is only present in very early ontogeny, and after a transition period gives way to learned object recognition mediated by cortical structures. • After the transition period, primate superior colliculi still function to provide unconscious innate stimulus recognition of the object’s class (prey vs. predator), and this recognition can still generate orienting and emotional response! • stop 1 4.5 BILLION years ago The Earth forms 2 1.5 3 Vertebrates originated about 525 million years ago (Cambrian explosion: twice complete genome duplication) 4 Dinosaurs originated ~230 million years ago 6 Primates originated ~70 million years ago 5 7 Human line split from chimpanzee line Modern humans: ~0.1 million YA 1. Hydra (relative of jellyfish) • • • • “…consciousness arises as a solution to one of the most fundamental problems facing any nervous system: Too much information constantly flows in to be fully processed. The brain evolved increasingly sophisticated mechanisms for deeply processing a few select signals at the expense of others… consciousness evolved gradually over the past half billion years and is present in a range of vertebrate species” “Even before the evolution of a central brain, nervous systems took advantage of a simple computing trick: competition. Neurons act like candidates in an election, each one shouting and trying to suppress its fellows. At any moment only a few neurons win that intense competition, their signals rising up above the noise and impacting the animal’s behavior. This process is called selective signal enhancement, and without it, a nervous system can do almost nothing.” When selective signal enhancement first evolved? “The hydra, a small relative of jellyfish, arguably has the simplest nervous system known—a nerve net. If you poke the hydra anywhere, it gives a generalized response. It shows no evidence of selectively processing some pokes while strategically ignoring others. The split between the ancestors of hydras and other animals, according to genetic analysis, may have been as early as 700 million years ago. Selective signal enhancement probably evolved after that.” 1cm 2. Arthropod compound eye • “The arthropod eye, on the other hand, has one of the best-studied examples of selective signal enhancement. It sharpens the signals related to visual edges and suppresses other visual signals, generating an outline sketch of the world.” • “Selective enhancement therefore probably evolved sometime between hydras and arthropods—between about 700 and 600 million years ago.” • “Selective signal enhancement is so primitive that it doesn’t even require a central brain. The eye, the network of touch sensors on the body, and the auditory system can each have their own local versions of attention focusing on a few select signals.” 3. Tectum - the centralized controller of attention • • • • “The next evolutionary advance was a centralized controller for attention that could coordinate among all senses. In many animals, that central controller is a brain area called the tectum. (“Tectum” means “roof” in Latin, and it often covers the top of the brain.) Tectum coordinates attention – aiming the satellite dishes of the eyes, ears, and nose toward anything important. All vertebrates (evolved 525 million years ago)—fish, reptiles, birds, and mammals—have a tectum; Tectum is absent from all invertebrates. Tectum “simulates the current state of the eyes, head, and other major body parts, making predictions about how these body parts will move next and about the consequences of their movement. For example, if you move your eyes to the right, the visual world should shift across your retinas to the left in a predictable way. The tectum compares the predicted visual signals to the actual visual input, to make sure that your movements are going as planned. ... In fish and amphibians, the tectum is the pinnacle of sophistication and the largest part of the brain. A frog has a pretty good simulation of itself.” Human brainstem with thalamus on top Cerebral cortex • • • • “The cortex is like an upgraded tectum. We still have a tectum buried under the cortex and it performs the same functions as in fish and amphibians. If you hear a sudden sound or see a movement in the corner of your eye, your tectum directs your gaze toward it quickly and accurately. The cortex also takes in sensory signals and coordinates movement, but it has a more flexible repertoire. ” Unlike the tectum, which models concrete objects like the eyes and the head, the cortex can model something much more abstract. ”We say we have consciousness because deep in the brain, something quite primitive is computing that semi-magical self-description. … and self-models become models of others.” “…consciousness arises as a solution to one of the most fundamental problems facing any nervous system: Too much information constantly flows in to be fully processed. The brain evolved increasingly sophisticated mechanisms for deeply processing a few select signals at the expense of others… consciousness evolved gradually over the past half billion years and is present in a range of vertebrate species”