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- Volume 31, 2008
Annual Review of Neuroscience - Volume 31, 2008
Volume 31, 2008
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Cerebellum-Like Structures and Their Implications for Cerebellar Function
Vol. 31 (2008), pp. 1–24More LessThe nervous systems of most vertebrates include both the cerebellum and structures that are architecturally similar to the cerebellum. The cerebellum-like structures are sensory structures that receive input from the periphery in their deep layers and parallel fiber input in their molecular layers. This review describes these cerebellum-like structures and compares them with the cerebellum itself. The cerebellum-like structures in three groups of fish act as adaptive sensory processors in which the signals conveyed by parallel fibers in the molecular layer predict the patterns of sensory input to the deep layers through a process of associative synaptic plasticity. Similarities between the cerebellum-like structures and the cerebellum suggest that the cerebellum may also generate predictions about expected sensory inputs or states of the system, as suggested also by clinical, experimental, and theoretical studies of the cerebellum. Understanding the process of predicting sensory patterns in cerebellum-like structures may therefore be a source of insight into cerebellar function.
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Spike Timing–Dependent Plasticity: A Hebbian Learning Rule
Natalia Caporale, and Yang DanVol. 31 (2008), pp. 25–46More LessSpike timing–dependent plasticity (STDP) as a Hebbian synaptic learning rule has been demonstrated in various neural circuits over a wide spectrum of species, from insects to humans. The dependence of synaptic modification on the order of pre- and postsynaptic spiking within a critical window of tens of milliseconds has profound functional implications. Over the past decade, significant progress has been made in understanding the cellular mechanisms of STDP at both excitatory and inhibitory synapses and of the associated changes in neuronal excitability and synaptic integration. Beyond the basic asymmetric window, recent studies have also revealed several layers of complexity in STDP, including its dependence on dendritic location, the nonlinear integration of synaptic modification induced by complex spike trains, and the modulation of STDP by inhibitory and neuromodulatory inputs. Finally, the functional consequences of STDP have been examined directly in an increasing number of neural circuits in vivo.
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Balancing Structure and Function at Hippocampal Dendritic Spines
Vol. 31 (2008), pp. 47–67More LessDendritic spines are the primary recipients of excitatory input in the central nervous system. They provide biochemical compartments that locally control the signaling mechanisms at individual synapses. Hippocampal spines show structural plasticity as the basis for the physiological changes in synaptic efficacy that underlie learning and memory. Spine structure is regulated by molecular mechanisms that are fine-tuned and adjusted according to developmental age, level and direction of synaptic activity, specific brain region, and exact behavioral or experimental conditions. Reciprocal changes between the structure and function of spines impact both local and global integration of signals within dendrites. Advances in imaging and computing technologies may provide the resources needed to reconstruct entire neural circuits. Key to this endeavor is having sufficient resolution to determine the extrinsic factors (such as perisynaptic astroglia) and the intrinsic factors (such as core subcellular organelles) that are required to build and maintain synapses.
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Place Cells, Grid Cells, and the Brain's Spatial Representation System
Vol. 31 (2008), pp. 69–89More LessMore than three decades of research have demonstrated a role for hippocampal place cells in representation of the spatial environment in the brain. New studies have shown that place cells are part of a broader circuit for dynamic representation of self-location. A key component of this network is the entorhinal grid cells, which, by virtue of their tessellating firing fields, may provide the elements of a path integration–based neural map. Here we review how place cells and grid cells may form the basis for quantitative spatiotemporal representation of places, routes, and associated experiences during behavior and in memory. Because these cell types have some of the most conspicuous behavioral correlates among neurons in nonsensory cortical systems, and because their spatial firing structure reflects computations internally in the system, studies of entorhinal-hippocampal representations may offer considerable insight into general principles of cortical network dynamics.
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Mitochondrial Disorders in the Nervous System
Vol. 31 (2008), pp. 91–123More LessMitochondrial diseases (encephalomyopathies) have traditionally been ascribed to defects of the respiratory chain, which has helped researchers explain their genetic and clinical complexity. However, other mitochondrial functions are greatly important for the nervous system, including protein importation, organellar dynamics, and programmed cell death. Defects in genes controlling these functions are attracting increasing attention as causes not only of neurological (and psychiatric) diseases but also of age-related neurodegenerative disorders. After discussing some pathogenic conundrums regarding the neurological manifestations of the respiratory chain defects, we review altered mitochondrial dynamics in the etiology of specific neurological diseases and in the physiopathology of more common neurodegenerative disorders.
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Vestibular System: The Many Facets of a Multimodal Sense
Vol. 31 (2008), pp. 125–150More LessElegant sensory structures in the inner ear have evolved to measure head motion. These vestibular receptors consist of highly conserved semicircular canals and otolith organs. Unlike other senses, vestibular information in the central nervous system becomes immediately multisensory and multimodal. There is no overt, readily recognizable conscious sensation from these organs, yet vestibular signals contribute to a surprising range of brain functions, from the most automatic reflexes to spatial perception and motor coordination. Critical to these diverse, multimodal functions are multiple computationally intriguing levels of processing. For example, the need for multisensory integration necessitates vestibular representations in multiple reference frames. Proprioceptive-vestibular interactions, coupled with corollary discharge of a motor plan, allow the brain to distinguish actively generated from passive head movements. Finally, nonlinear interactions between otolith and canal signals allow the vestibular system to function as an inertial sensor and contribute critically to both navigation and spatial orientation.
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Role of Axonal Transport in Neurodegenerative Diseases*
Vol. 31 (2008), pp. 151–173More LessMany major human neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS), display axonal pathologies including abnormal accumulations of proteins and organelles. Such pathologies highlight damage to the axon as part of the pathogenic process and, in particular, damage to transport of cargoes through axons. Indeed, we now know that disruption of axonal transport is an early and perhaps causative event in many of these diseases. Here, we review the role of axonal transport in neurodegenerative disease.
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Active and Passive Immunotherapy for Neurodegenerative Disorders
Vol. 31 (2008), pp. 175–193More LessImmunotherapeutic strategies to combat neurodegenerative disorders have galvanized the scientific community since the first dramatic successes in mouse models recreating aspects of Alzheimer disease (AD) were reported. However, initial human trials of active amyloid-beta (Aβ) vaccination were halted early because of a serious safety issue: meningoencephalitis in 6% of subjects. Nonetheless, some encouraging preliminary data were obtained, and rapid progress has been made toward developing alternative, possibly safer active and passive immunotherapeutic approaches for several neurodegenerative conditions. Many of these are currently in human trials for AD. Despite these advances, our understanding of the essential mechanisms underlying the effects seen in preclinical models and human subjects is still incomplete. Antibody-induced phagocytosis of pathological protein deposits, direct antibody-mediated disruption of aggregates, neutralization of toxic soluble proteins, a shift in equilibrium toward efflux of specific proteins from the brain, cell-mediated immune responses, and other mechanisms may all play roles depending on the specific immunotherapeutic scenario.
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Descending Pathways in Motor Control
Vol. 31 (2008), pp. 195–218More LessEach of the descending pathways involved in motor control has a number of anatomical, molecular, pharmacological, and neuroinformatic characteristics. They are differentially involved in motor control, a process that results from operations involving the entire motor network rather than from the brain commanding the spinal cord. A given pathway can have many functional roles. This review explores to what extent descending pathways are highly conserved across species and concludes that there are actually rather widespread species differences, for example, in the transmission of information from the corticospinal tract to upper limb motoneurons. The significance of direct, cortico-motoneuronal (CM) connections, which were discovered a little more than 50 years ago, is reassessed. I conclude that although these connections operate in parallel with other less direct linkages to motoneurons, CM influence is significant and may subserve some special functions including adaptive motor behaviors involving the distal extremities.
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Task Set and Prefrontal Cortex
Vol. 31 (2008), pp. 219–245More LessA task set is a configuration of cognitive processes that is actively maintained for subsequent task performance. Single-unit and brain-imaging studies have identified the neural correlates for task sets in the prefrontal cortex. Here I examine whether the neural data obtained thus far are sufficient to explain the behaviors that have been illustrated within the conceptual framework of task sets. I first discuss the selectivity of neural activity in representing a specific task. I then discuss the competitions between neural representations of task sets during task switch. Finally I discuss how, in neural terms, a task set is implemented to facilitate task performance. The processes of representing, updating, and implementing task sets occur in parallel at multiple levels of brain organization. Neural accounts of task sets demonstrate that the brain determines our thoughts and behaviors.
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Multiple Sclerosis: An Immune or Neurodegenerative Disorder?
Vol. 31 (2008), pp. 247–269More LessMultiple sclerosis (MS) is an inflammatory-mediated demyelinating disease of the human central nervous system. The clinical disease course is variable, usually starts with reversible episodes of neurological disability in the third or fourth decade of life, and transforms into a disease of continuous and irreversible neurological decline by the sixth or seventh decade. We review data that support neurodegeneration as the major cause of irreversible neurological disability in MS patients. We question whether inflammatory demyelination is primary or secondary in the disease process and discuss the challenges of elucidating the cause of MS and developing therapies that will delay or prevent the irreversible and progressive neurological decline that most MS patients endure.
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Multifunctional Pattern-Generating Circuits
Vol. 31 (2008), pp. 271–294More LessThe ability of distinct anatomical circuits to generate multiple behavioral patterns is widespread among vertebrate and invertebrate species. These multifunctional neuronal circuits are the result of multistable neural dynamics and modular organization. The evidence suggests multifunctional circuits can be classified by distinct architectures, yet the activity patterns of individual neurons involved in more than one behavior can vary dramatically. Several mechanisms, including sensory input, the parallel activity of projection neurons, neuromodulation, and biomechanics, are responsible for the switching between patterns. Recent advances in both analytical and experimental tools have aided the study of these complex circuits.
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Retinal Axon Growth at the Optic Chiasm: To Cross or Not to Cross
Vol. 31 (2008), pp. 295–315More LessAt the optic chiasm, retinal ganglion cell axons from each eye converge and segregate into crossed and uncrossed projections, a pattern critical for binocular vision. Here, we review recent findings on optic chiasm development, highlighting the specific transcription factors and guidance cues that implement retinal axon divergence into crossed and uncrossed pathways. Although mechanisms underlying the formation of the uncrossed projection have been identified, the means by which retinal axons are guided across the midline are still unclear. In addition to directives provided by transcription factors and receptors in the retina, gene expression in the ventral diencephalon influences chiasm formation. Throughout this review, we compare guidance mechanisms at the optic chiasm with those in other midline models and highlight unanswered questions both for retinal axon growth and axon guidance in general.
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Brain Circuits for the Internal Monitoring of Movements*
Vol. 31 (2008), pp. 317–338More LessEach movement we make activates our own sensory receptors, thus causing a problem for the brain: the spurious, movement-related sensations must be discriminated from the sensory inputs that really matter, those representing our environment. Here we consider circuits for solving this problem in the primate brain. Such circuits convey a copy of each motor command, known as a corollary discharge (CD), to brain regions that use sensory input. In the visual system, CD signals may help to produce a stable visual percept from the jumpy images resulting from our rapid eye movements. A candidate pathway for providing CD for vision ascends from the superior colliculus to the frontal cortex in the primate brain. This circuit conveys warning signals about impending eye movements that are used for planning subsequent movements and analyzing the visual world. Identifying this circuit has provided a model for studying CD in other primate sensory systems and may lead to a better understanding of motor and mental disorders.
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Wnt Signaling in Neural Circuit Assembly
Vol. 31 (2008), pp. 339–358More LessThe Wnt family of secreted proteins plays a crucial role in nervous system wiring. Wnts regulate neuronal positioning, polarization, axon and dendrite development, and synaptogenesis. These diverse roles of Wnt proteins are due not only to the large numbers of Wnt ligands and receptors but also to their ability to signal through distinct signaling pathways in different cell types and developmental contexts. Studies on Wnts have shed new light on novel molecular mechanisms that control the development of complex neuronal connections. This review discusses recent advances on how Wnt signaling influences different aspects of neuronal circuit assembly through changes in gene expression and/or cytoskeletal modulation.
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Habits, Rituals, and the Evaluative Brain
Vol. 31 (2008), pp. 359–387More LessScientists in many different fields have been attracted to the study of habits because of the power habits have over behavior and because they invoke a dichotomy between the conscious, voluntary control over behavior, considered the essence of higher-order deliberative behavioral control, and lower-order behavioral control that is scarcely available to consciousness. A broad spectrum of behavioral routines and rituals can become habitual and stereotyped through learning. Others have a strong innate basis. Repetitive behaviors can also appear as cardinal symptoms in a broad range of neurological and neuropsychiatric illness and in addictive states. This review suggests that many of these behaviors could emerge as a result of experience-dependent plasticity in basal ganglia–based circuits that can influence not only overt behaviors but also cognitive activity. Culturally based rituals may reflect privileged interactions between the basal ganglia and cortically based circuits that influence social, emotional, and action functions of the brain.
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Mechanisms of Self-Motion Perception
Vol. 31 (2008), pp. 389–410More LessGuiding effective movement through the environment is one of the visual system's most important functions. The pattern of motion that we see allows us to estimate our heading accurately in a variety of environments, despite the added difficulty imposed by our own eye and head movements. The cortical substrates for heading perception include the medial superior temporal area (MST) and the ventral intraparietal area (VIP). This review discusses recent work on these two areas in the context of behavioral observations that establish the important problems the visual system must solve. Signals relevant to self motion are both more widespread than heretofore recognized and also more complex because they are multiplexed with other sensory signals, such as vestibular, auditory, and tactile information. The review presents recent work as a background to highlight important problems that remain unsolved.
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Mechanisms of Face Perception
Vol. 31 (2008), pp. 411–437More LessFaces are among the most informative stimuli we ever perceive: Even a split-second glimpse of a person's face tells us his identity, sex, mood, age, race, and direction of attention. The specialness of face processing is acknowledged in the artificial vision community, where contests for face-recognition algorithms abound. Neurological evidence strongly implicates a dedicated machinery for face processing in the human brain to explain the double dissociability of face- and object-recognition deficits. Furthermore, recent evidence shows that macaques too have specialized neural machinery for processing faces. Here we propose a unifying hypothesis, deduced from computational, neurological, fMRI, and single-unit experiments: that what makes face processing special is that it is gated by an obligatory detection process. We clarify this idea in concrete algorithmic terms and show how it can explain a variety of phenomena associated with face processing.
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The Prion's Elusive Reason for Being
Vol. 31 (2008), pp. 439–477More LessThe protein-only hypothesis posits that the infectious agent causing transmissible spongiform encephalopathies consists of protein and lacks any informational nucleic acids. This agent, termed prion by Stanley Prusiner, is thought to consist partly of PrPSc, a conformational isoform of a normal cellular protein termed PrPC. Scientists and lay persons have been fascinated by the prion concept, and it has been subjected to passionate critique and intense experimental scrutiny. As a result, PrPC and its isoforms rank among the most intensively studied proteins encoded by the mammalian genome. Despite all this research, both the physiological function of PrPC and the molecular pathways leading to neurodegeneration in prion disease remain unknown. Here we review the salient traits of those diseases ascribed to improper behavior of the prion protein and highlight how the physiological functions of PrPC may help explain the toxic phenotypes observed in prion disease.
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Mechanisms Underlying Development of Visual Maps and Receptive Fields
Vol. 31 (2008), pp. 479–509More LessPatterns of synaptic connections in the visual system are remarkably precise. These connections dictate the receptive field properties of individual visual neurons and ultimately determine the quality of visual perception. Spontaneous neural activity is necessary for the development of various receptive field properties and visual feature maps. In recent years, attention has shifted to understanding the mechanisms by which spontaneous activity in the developing retina, lateral geniculate nucleus, and visual cortex instruct the axonal and dendritic refinements that give rise to orderly connections in the visual system. Axon guidance cues and a growing list of other molecules, including immune system factors, have also recently been implicated in visual circuit wiring. A major goal now is to determine how these molecules cooperate with spontaneous and visually evoked activity to give rise to the circuits underlying precise receptive field tuning and orderly visual maps.
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Previous Volumes
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Volume 47 (2024)
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Volume 46 (2023)
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Volume 45 (2022)
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Volume 44 (2021)
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Volume 43 (2020)
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Volume 42 (2019)
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Volume 41 (2018)
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Volume 40 (2017)
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Volume 39 (2016)
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Volume 38 (2015)
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Volume 37 (2014)
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Volume 36 (2013)
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Volume 35 (2012)
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Volume 34 (2011)
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Volume 33 (2010)
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Volume 32 (2009)
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Volume 31 (2008)
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Volume 30 (2007)
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Volume 29 (2006)
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Volume 28 (2005)
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Volume 27 (2004)
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Volume 26 (2003)
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Volume 25 (2002)
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Volume 24 (2001)
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Volume 23 (2000)
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Volume 22 (1999)
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Volume 21 (1998)
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Volume 20 (1997)
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Volume 19 (1996)
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Volume 18 (1995)
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Volume 17 (1994)
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Volume 16 (1993)
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Volume 15 (1992)
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Volume 14 (1991)
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Volume 13 (1990)
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Volume 12 (1989)
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Volume 11 (1988)
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Volume 10 (1987)
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Volume 9 (1986)
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Volume 8 (1985)
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Volume 7 (1984)
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Volume 6 (1983)
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Volume 5 (1982)
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Volume 4 (1981)
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Volume 3 (1980)
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Volume 2 (1979)
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Volume 1 (1978)
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Volume 0 (1932)