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- Field Chair of Ophthalmologic Research, Professor and Head, Department of Ophthalmology and Visual Sciences, University of Illinois Eye and Ear Infirmary, Chicago, IL, USA
Lower: When a lateral appendage contacts an object of interest arteria del corazon purchase 75 mg triamterene mastercard, the nose shifts to blood pressure wrist monitor buy generic triamterene 75 mg line touch it with no jack mack the heart attack i39m gonna be somebody discount 75mg triamterene with visa. So the collicular mechanism for orienting the sensors needs to pulse pressure 56 purchase triamterene 75mg otc be informed by many issues. Decisions regarding where to look are made at the cortical level, which requires the cerebral cortex to communicate with the superior colliculus. The upper collicular layers receive visual patterns and relay upward for further processing by cortical areas concerned with motion, and they receive signals from the same areas (Berman & Wurtz, 2010). The deeper collicular layers collect signals from the highest executive levels-frontal and parietal cortex-which convey a highly informed decision regarding where to look. The computations needed to reach that decision are extensive, involving much of the brain. But the decision can be relayed to the superior colliculus via a rather modest tract that requires only 6% of the corticocollicular pathway (Collins et al. In short, the deeper layers of the colliculus know where to direct the eyes-that circuit is hardwired between the motor map and the low-level pattern generators that coordinate eye muscles. The deeper layers learn whether to move the eyes and when, by integrating raw-ish sensory inputs15 with processed signals descending from cortex. The integrated output delivers instructions regarding vector and timing to pattern generators in brainstem that micromanage eye movements, and to those in the upper spinal cord that micromanage head movements. Thus, the descending collicular tract resembles various other tracts, such as fornix, hypothalamic, optic, and corticospinal, in being organized to send minimal instructions. It is tweaked by succinct executive decisions from above and delivers succinct instructions to low-level pattern generators. But it must also fulfill one more responsibility-to inform higher levels that its order: "Look! Corollary Discharge, When the retina is swept passively across a scene, the scene appears to move. The reader can confirm this by closing one eye and jiggling the other with a forefinger (gently! However, when the superior colliculus orders the eye to sweep actively, the scene appears stable. The trick to stabilizing the scene when the brain moves the eye is to relay the order: "move! These areas, lying anteriorly in the parietal and prefrontal cortex (frontal eye field), know where the eye is looking-but they also need to know where the eye is about to look, so that they can compensate in advance before the motion occurs. This prediction, by allowing compensation, stablilizes perception-when we move our eyes, the world appears to remain stationary, as it should (Sommer & Wurtz, 2008; Wurtz et al. The anterior frontal cortex is as far away from the superior colliculus as it is possible to be, so one might wonder why spend so much wire One reason is that large patterns are assembled step-wise by cortical areas that press ever forward (chapter 12). By the stage where behaviorally relevant patterns have been assembled, compared to stores, and readied for use in selecting an action, the anterior frontal lobe is pretty much the last bit of available real estate. Moreover, because this cortical region decides where to look, it is precisely the site that needs corollary discharge to compensate for self-motion. Another reason to control eye movements from the anterior frontal lobe is that, beyond their aid to sensing, eye movements also serve social communication. Even a dog notices and becomes aggressive when stared down by an unfamiliar human. Thus, as the cortical areas for social communication expand in the frontal and temporal lobes (chapter 12), they require a mechanism for sending executive summaries down to the superior colliculus. So design again economizes by using long pathways to send modest messages: "Look here! How Bigger Brains Are Organized 83 In summary, to build efficient sensors, the brain makes them mobile. It also compensates for self-induced motion, targeting the highest levels where choices and actions are being selected. These high-level mechanisms can then efficiently direct the low-level circuits that generate stereotyped patterns of movement. These circuits use modest tracts to govern low-level pattern generators located near the relevant motor neuron clusters.
Search for the oscillators Early studies of animal locomotion were fraught with bitter argument about the origins of cyclical activity-such as stepping blood pressure extremely low 75 mg triamterene. Oscillations might be produced within the nervous system by local circuits (central pattern generators) blood pressure young age order 75 mg triamterene mastercard. Or they might be produced outside the nervous system by cycling sensory feedback (Marder & Bucher heart attack quizlet generic 75mg triamterene visa, 2001; Goulding hypertension zone tool generic triamterene 75 mg free shipping, 2009). This activates sensors that inhibit the extensor motor neurons and excite the flexor motor neurons, thus retracting the limb. Flexion activates sensors that inhibit the flexor motor neurons and excite the extensor neurons, and so on. A central pattern generator sends cyclical commands to the motor neurons, and sensory feedback adjusts their phase, frequency, and amplitude to match changes in external load (Burrows, 1996). Worms are capable of making central pattern generators-some of their cells use internal biochemical oscillators to control the rhythmical movements of ingestion, defecation, and copulation. That the worm can make central pattern generators but does not do so for locomotion suggests that it might have found a better way. Rather than relying on a pattern generator in its brain, the worm exploits its body. Cycling with the body the worm builds its oscillator by combining feedback with body mechanics. Sensors excited by these forces feed back to inhibit motor neurons, whereupon the muscles relax and the body springs back. This terminates the negative feedback, allowing the motor neurons to reactivate and start a new cycle (figure 2. Engineers call this embodied computation (also embodied intelligence or cognition; Pfeifer & Bongard, 2006). In the early days of robots, crawling and stepping movements were generated by an all-powerful central computer-an omniscient central pattern generator. To implement this top-down design required the robot to drag around a heavy computer, which, in turn, meant thicker limbs and stronger actuators-the result, a power-hungry behemoth. It was eventually realized that the robot and its limbs are a computer, an analogue computer that runs its mechanics in real time (Brooks, 1990). This analogue computer comes for free and can be set up to process information for control by, for example, being part of an oscillator. This insight inspired a new generation of small, efficient, and adroit stepping machines that blew away the behemoths. Thus, the worm exemplifies embodied computation with a neuromechanical system that matches and integrates a few basic components to meet specifications efficiently. Neural circuits coordinate patterns of movement Despite the contribution of body mechanics to the oscillator, neural circuits are still essential-they close the loop inside the worm. The neural circuits must be correctly configured and tuned to work with the biomechanics. Sensors must give the right feedback to motor neurons, and motor neurons must send the right signals to the right muscles with the right timing. Circuits are constructed to make this happen by ensuring that as muscles on one side of the body contract, the antagonistic muscles on the other side relax: motor neurons on one side inhibit the excitatory motor neurons for the antagonists and also excite their inhibitory motor neurons (figure 2. Here, then, is a circuit motif, reciprocal inhibition (Sherrington, 1906), that is widely employed in brains because it simply and effectively solves a common problem. Changing direction the brain produces motor rhythms for "forward" and "backward" using two separate sets of motor neurons. Each set has its own circuit: one works with the biomechanics to send the undulatory wave head-to-tail and the Why an Animal Needs a Brain 27 other works to send the wave tail-to-head. Most animals use a single set of motor neurons as the final common pathway for all commands to muscle. Using two independent sets, each with a full complement of connections and synapses to muscles, seems wasteful, so why does the worm do this We speculate that for a small brain with neuromechanical oscillation, two sets of motor neurons are cheaper than a complicated central pattern generator. Equipped to move further and faster, its costs are higher and the risks greater, but so are the opportunities and rewards. So the acts must be directed appropriately (de Bono & Maricq, 2005; Lockery, 2011). Mechanosensory neurons at the front drive interneurons that activate the "backward" set of motor neurons, and mechanosensory neurons at the rear drive interneurons that activate the "forward" set.
Rather pulse pressure waveform cheap 75 mg triamterene with visa, experience is what we have when we push against the world and the world pushes back arteria espinal anterior order triamterene 75 mg mastercard. It may sometimes be the case that when I act in a certain way blood pressure chart free printable triamterene 75mg low price, the world puts me into a certain state how quickly do blood pressure medication work cheap triamterene 75mg overnight delivery. It seems attractive to say that vision typically involves the experience of a whole range of things in front of the perceiver, only some of which at any one time are the object of attention. As you explore the scene in front of you, "each thing you ask yourself about springs into awareness" (target article, sect. Before you ask about a particular feature (or direct your attention it), the information about it is "out there" and obtainable "by making the appropriate eye movement or attention shift," but, the authors insist, the information is at the earlier time "not currently available. But they evidently want to go further, and deny that I was even aware of the paper before I was actually attending to it. We are under "the impression of seeing everything," but "only a small fragment of the world is actually being seen" (sect. And the source of the mistake is that we confuse being able to see x with actually seeing x (sect. When we have "continuous access to environmental detail," we all too readily suppose we have "continuous representation of that detail" (sect. Since presumably we only attend to a few things at a time, it is as though we see through a narrow tube of attentional consciousness, never perceiving more than is currently in the attentional field. And if my attention is newly drawn to something, it can only be to something I am not already seeing. This is extremely implausible: surely while looking at and thinking of the books in front of me, I can also be aware of the paper off to the left. If someone moves the paper, I can easily be aware of this (even while keeping my eyes on the books. The authors claim that before I actually attend to the object, information is "out there" but "cannot at this moment be used to control judgments and utterances" (sect. I can surely comment on gross features like the approximate size and orientation of the paper, and perhaps its color. If the authors insist that one simply cannot make a judgment about something without at that moment "attending to" it (just by virtue of thinking of it), then that again seems incorrect. Suppose that at time t1 I look at my books, and am rather indistinctly aware of the paper off to the left; then I close my eyes and make a judgment at time t2 about the color of the paper I saw shortly before. Indeed at t2 I will be "attending" to the paper, but that hardly implies that at t1 I was doing so already. Thus, in my opinion, O&N are too quick to dismiss the idea of simultaneous visual representation of things, only some of which are attended to. It is true that we should not mistake mere availability of information for its actual supply; but we must also avoid the converse mistake. In fact what we need is to allow that, just as information from the things we see may vary greatly in degree of detail, so also visual experience will vary greatly in degree of detail (whether or not that experience is ultimately to be described in terms of pictorial representation. O&N offer several examples to confirm their idea that we often look at something without seeing it. The intention, I think, is to discredit representationalist views that would be forced to say that an item was "seen" simply because it was within the field of view. Writing the sentence out accurately could be a sign that the letters had been seen, yet might still be followed by failure in the counting task. In general, anyone who believes in representations (whether "in the mind" or "in the brain") will surely give a role not only to visual representation but also to (various forms of) something like inference and conceptual interpretation. Under particular circumstances, a person may be unaware of a change, even quite a large one, in the scene before her. But is this definitely a case where the person does not "see" something in the visual field We need to distinguish between seeing the change and seeing the objects in view before and after the change.
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Etiology of parasomnias such as nightmare disorder arrhythmia flashcards 75 mg triamterene sale, sleep terror and sleepwalking disorders is unknown blood pressure chart over 65 proven triamterene 75mg. Psychological techniques such as relaxation or stimulus control and change in habits D nqf 0013 hypertension generic 75mg triamterene fast delivery. Compare the treatments for anorexia nervosa blood pressure normal or high buy triamterene 75mg with amex, bulimia nervosa, and binge-eating disorder. Discuss the characteristics, etiology, and treatment of primary sleep disorders (pp. A major irony of anorexia nervosa and bulimia nervosa are that they occur in times and places of relative affluence (consider the "vomitoria" of ancient Rome where wealthy Romans would go to purge after binging on lavish feasts). Such a pattern would logically suggest that these eating disorders are socially and culturally influenced. A team of investigators at the Howard Hughes Medical Institute and the University of Texas Southwestern Medical Center isolated the hormones, which they call orexin A and orexin B (orexis means "appetite" in Greek). Anorexia and bulimia are difficult disorders to deal with, even for professionals; typically waiting it out is not an option, while insisting that the person get help is likely to result in withdrawal. You may want to encourage the person to contact you when there is the need to talk to someone. However, there is a lot to gain by the process and a lot to lose if the choice is made to continue the existing behaviors. Chapter 18 discusses legal and ethical issues involved in providing therapy to persons who do not want to accept treatment. As discussed in the chapter, the first step in treating anorexia is weight gain, and often this means use of a feeding tube to force feed the patient. The insidious nature of anorexia creates strong resistance to weight gain and all strategies to promote weight gain, even in the face of permanent, lifelong physical ailments and even death. Have each student write on a piece of paper any sleep problems they have had in the recent past with sleep. At the end of lecture give names and contact information of professionals at your school or in the community who specialize in sleep disorders. In small groups, have students put together presentations that demonstrate the effect of the media on body image and eating disorders, then have them present a plan to counteract these powerful forces. After completing the presentations, the class as a whole, could design an intervention to present to junior high school and high school classes to educate students about the problem and prevention. Have your students develop and administer a weight satisfaction survey in which they collect data from males and females ranging in age from preteen to early adulthood, from different 2. Responses from the entire class can be analyzed statistically and compared with research presented in the text. The results of the survey and data analysis can be used to develop presentations for local schools and other community organizations. A large-scale (N = 3,175) survey of middle-school children found that more than 40 percent reported feeling fat and wishing to lose weight. Among girls, whose average age was 12, 43 percent had dieted, 11 percent had fasted, and 6 percent had made themselves vomit to lose weight (Childress et al. It involves a tendency to restrain oneself from eating for fear of gaining weight. People with clinical eating disorders and "normal" people can be restrained eaters. They diet frequently and, when feeling susceptible to stress or negative emotions, binge rather than eat normally. It is useful in helping students look at their attitudes and behaviors relevant to eating, but many other sources of information are needed before concluding that high scorers have a problem. Reprinted with permission from the American Psychological Association and the author. Add your total points: If your total score is 14 or more points, you have a tendency to be a restrained eater. This documentary shows interviews with four anorexic adolescent girls who describe their self-starvation and their attempts to overcome their obsession with thinness. Provides information about anorexia and follows a young women as she battles anorexia. Effective with depression; may alter cortisol levels; concern over side effects; drugs used instead B.
When a natural scene video was presented repeatedly blood pressure garlic discount triamterene 75 mg with visa, a high-frequency feature (downward arrow) evoked bursts of synaptic quanta to blood pressure 60 0 triamterene 75 mg without a prescription the brisk-transient cell but not the localedge cell arteria differential purchase triamterene 75mg with amex. A low-frequency feature heart attack gun purchase triamterene 75mg mastercard, an edge going dark then bright (upward arrow), evoked a burst of quanta to the local-edge cell. Principles of Retinal Design 313 Why types are conserved One reason why ganglion cell types are conserved types across habitat and lifestyle is that physical properties, such as photon noise, vesicle noise, diffusion speed, synapse size, and so on are invariant. Therefore, a mouse eye can shrink the number of neurons compared to a cow eye, but it cannot greatly shrink either the neurons themselves or their synapses. All scenes contain mostly low temporal and low spatial frequencies in the same relative amounts; moreover, they are scale invariant and thus unchanging as a pattern moves closer or farther away, or as a pattern is magnified on the retina of a larger eye. The same is true for various motions that sweep, jump, track, or jiggle patterns across the retina: their distributions of temporal and spatial frequencies are all the same (figure 11. Considering that retinal circuits are selected to encode optimally, once they reach the point of optimality-where costs just balance benefits- there is no pressure for change but instead pressure to preserve what works. The many types of interneuron are also conserved because they help create ganglion cell types. Dendritic field sizes are conserved across species due to the invariance of various physical factors upon which the neurons rely. Scene statistics, photon noise, diffusion distances and speeds, synapse size, receptor binding properties, and channel properties are the same for mouse and human. Consequently, a local-edge cell, to fill its coding capacity, must spread its dendrites sufficiently for its overlying patch of cones to capture sufficient photons. And it must branch the dendrites sufficiently for the membrane to capture sufficient synapses. The hawk has greater acuity because of optical factors and higher density of photoreceptors, but the mouse casts a smaller image. Thus, as the two species track each other, they will both use the local-edge type of ganglion cell. Species may have opposite goals, but when the images are similar, they use the same cell type. This requires a stringently tuned nonlinear filter to selectively amplify the signal (Rieke et al. A stringent filter applied to a natural scene would reject most information, so a ganglion cell would be mostly silent. Reprinted with modifications and permission from Balasubramanian & Sterling (2009); data are from Koch et al. Thus, the uniformity of natural scene statistics restrains the specificity of ganglion cell tuning and thereby reduces the number of types. This leads to a dual design: some nonstringent filters to capture the broad distribution of spatial and temporal frequencies in natural scenes, and some quasi-stringent filters to match stereotyped aspects present in most scenes that are needed by various downstream users. Small ganglion cells have more noise, and large ganglion cells have more redundancy (Koch et al. The quasi-stringent types fill capacity to the same extent as the nonstringent types. Thus, they are no more efficient than the nonstringent types, as would be expected because they share the same noisy inputs. However, the quasi-stringent types do manage to delete certain signals that their specific downstream targets will not need. Since all scenes contain similar distributions of spatial and temporal frequencies, each type responds similarly to all scenes (figure 11. Initially this seems surprising since the traditional experiment searches for particular 316 Chapter 11 stimuli that a cell "likes best," leading to the idea of ganglion cells as "feature detectors. Why some types are more selective the nonstringent strategy employs five types to parcel the natural distribution of achromatic spatial and temporal frequencies, plus one more to parcel the spectral frequencies. Among the low-level users of retinal information are central pattern generators that coordinate motion of the eyes and head. All pattern generators require feedback that, as chapter 4 noted, is obtained most efficiently from sensors that send only what is needed to correct the output. To supply several of these low-level mechanisms, the retina constructs directionalselective ganglion cells-and not just one type, but three types that together cover the retina with 10 separate arrays.