Browsing by Subject "Neural Pathways"

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    A Diffusion MRI Tractography Connectome of the Mouse Brain and Comparison with Neuronal Tracer Data.
    (Cereb Cortex, 2015-11) Calabrese, Evan; Badea, Alexandra; Cofer, Gary; Qi, Yi; Johnson, G Allan
    Interest in structural brain connectivity has grown with the understanding that abnormal neural connections may play a role in neurologic and psychiatric diseases. Small animal connectivity mapping techniques are particularly important for identifying aberrant connectivity in disease models. Diffusion magnetic resonance imaging tractography can provide nondestructive, 3D, brain-wide connectivity maps, but has historically been limited by low spatial resolution, low signal-to-noise ratio, and the difficulty in estimating multiple fiber orientations within a single image voxel. Small animal diffusion tractography can be substantially improved through the combination of ex vivo MRI with exogenous contrast agents, advanced diffusion acquisition and reconstruction techniques, and probabilistic fiber tracking. Here, we present a comprehensive, probabilistic tractography connectome of the mouse brain at microscopic resolution, and a comparison of these data with a neuronal tracer-based connectivity data from the Allen Brain Atlas. This work serves as a reference database for future tractography studies in the mouse brain, and demonstrates the fundamental differences between tractography and neuronal tracer data.
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    A pathway in primate brain for internal monitoring of movements.
    (Science, 2002-05-24) Sommer, Marc A; Wurtz, Robert H
    It is essential to keep track of the movements we make, and one way to do that is to monitor correlates, or corollary discharges, of neuronal movement commands. We hypothesized that a previously identified pathway from brainstem to frontal cortex might carry corollary discharge signals. We found that neuronal activity in this pathway encodes upcoming eye movements and that inactivating the pathway impairs sequential eye movements consistent with loss of corollary discharge without affecting single eye movements. These results identify a pathway in the brain of the primate Macaca mulatta that conveys corollary discharge signals.
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    Activation in mesolimbic and visuospatial neural circuits elicited by smoking cues: evidence from functional magnetic resonance imaging.
    (Am J Psychiatry, 2002-06) Due, Deborah L; Huettel, Scott A; Hall, Warren G; Rubin, David C
    OBJECTIVE: The authors sought to increase understanding of the brain mechanisms involved in cigarette addiction by identifying neural substrates modulated by visual smoking cues in nicotine-deprived smokers. METHOD: Event-related functional magnetic resonance imaging (fMRI) was used to detect brain activation after exposure to smoking-related images in a group of nicotine-deprived smokers and a nonsmoking comparison group. Subjects viewed a pseudo-random sequence of smoking images, neutral nonsmoking images, and rare targets (photographs of animals). Subjects pressed a button whenever a rare target appeared. RESULTS: In smokers, the fMRI signal was greater after exposure to smoking-related images than after exposure to neutral images in mesolimbic dopamine reward circuits known to be activated by addictive drugs (right posterior amygdala, posterior hippocampus, ventral tegmental area, and medial thalamus) as well as in areas related to visuospatial attention (bilateral prefrontal and parietal cortex and right fusiform gyrus). In nonsmokers, no significant differences in fMRI signal following exposure to smoking-related and neutral images were detected. In most regions studied, both subject groups showed greater activation following presentation of rare target images than after exposure to neutral images. CONCLUSIONS: In nicotine-deprived smokers, both reward and attention circuits were activated by exposure to smoking-related images. Smoking cues are processed like rare targets in that they activate attentional regions. These cues are also processed like addictive drugs in that they activate mesolimbic reward regions.
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    Adult age differences in frontostriatal representation of prediction error but not reward outcome.
    (Cogn Affect Behav Neurosci, 2014-06) Samanez-Larkin, Gregory R; Worthy, Darrell A; Mata, Rui; McClure, Samuel M; Knutson, Brian
    Emerging evidence from decision neuroscience suggests that although younger and older adults show similar frontostriatal representations of reward magnitude, older adults often show deficits in feedback-driven reinforcement learning. In the present study, healthy adults completed reward-based tasks that did or did not depend on probabilistic learning, while undergoing functional neuroimaging. We observed reductions in the frontostriatal representation of prediction errors during probabilistic learning in older adults. In contrast, we found evidence for stability across adulthood in the representation of reward outcome in a task that did not require learning. Together, the results identify changes across adulthood in the dynamic coding of relational representations of feedback, in spite of preserved reward sensitivity in old age. Overall, the results suggest that the neural representation of prediction error, but not reward outcome, is reduced in old age. These findings reveal a potential dissociation between cognition and motivation with age and identify a potential mechanism for explaining changes in learning-dependent decision making in old adulthood.
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    Adult age differences in functional connectivity during executive control.
    (Neuroimage, 2010-08-15) Madden, David J; Costello, Matthew C; Dennis, Nancy A; Davis, Simon W; Shepler, Anne M; Spaniol, Julia; Bucur, Barbara; Cabeza, Roberto
    Task switching requires executive control processes that undergo age-related decline. Previous neuroimaging studies have identified age-related differences in brain activation associated with global switching effects (dual-task blocks versus single-task blocks), but age-related differences in activation during local switching effects (switch trials versus repeat trials, within blocks) have not been investigated. This experiment used functional magnetic resonance imaging (fMRI), and diffusion tensor imaging (DTI), to examine adult age differences in task switching across adjacent trials (i.e., local task switching). During fMRI scanning, participants performed a cued, word categorization task. From interspersed cue-only trials, switch-related processing associated with the cue was estimated separately from the target. Activation associated with task switching, within a distributed frontoparietal network, differed for cue- and target-related processing. The magnitude of event-related activation for task switching was similar for younger adults (n=20; 18-27years) and older adults (n=20; 60-85years), although activation sustained throughout the on-tasks periods exhibited some age-related decline. Critically, the functional connectivity of switch-related regions, during cue processing, was higher for younger adults than for older adults, whereas functional connectivity during target processing was comparable across the age groups. Further, individual differences in cue-related functional connectivity shared a substantial portion of the age-related variability in the efficiency of target categorization response (drift rate). This age-related difference in functional connectivity, however, was independent of white matter integrity within task-relevant regions. These findings highlight the functional connectivity of frontoparietal activation as a potential source of age-related decline in executive control.
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    Advances in understanding mechanisms of thalamic relays in cognition and behavior.
    (J Neurosci, 2014-11-12) Mitchell, Anna S; Sherman, S Murray; Sommer, Marc A; Mair, Robert G; Vertes, Robert P; Chudasama, Yogita
    The main impetus for a mini-symposium on corticothalamic interrelationships was the recent number of studies highlighting the role of the thalamus in aspects of cognition beyond sensory processing. The thalamus contributes to a range of basic cognitive behaviors that include learning and memory, inhibitory control, decision-making, and the control of visual orienting responses. Its functions are deeply intertwined with those of the better studied cortex, although the principles governing its coordination with the cortex remain opaque, particularly in higher-level aspects of cognition. How should the thalamus be viewed in the context of the rest of the brain? Although its role extends well beyond relaying of sensory information from the periphery, the main function of many of its subdivisions does appear to be that of a relay station, transmitting neural signals primarily to the cerebral cortex from a number of brain areas. In cognition, its main contribution may thus be to coordinate signals between diverse regions of the telencephalon, including the neocortex, hippocampus, amygdala, and striatum. This central coordination is further subject to considerable extrinsic control, for example, inhibition from the basal ganglia, zona incerta, and pretectal regions, and chemical modulation from ascending neurotransmitter systems. What follows is a brief review on the role of the thalamus in aspects of cognition and behavior, focusing on a summary of the topics covered in a mini-symposium held at the Society for Neuroscience meeting, 2014.
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    Altered resting-state functional connectivity of basolateral and centromedial amygdala complexes in posttraumatic stress disorder.
    (Neuropsychopharmacology, 2014-01) Brown, Vanessa M; LaBar, Kevin S; Haswell, Courtney C; Gold, Andrea L; Mid-Atlantic MIRECC Workgroup; McCarthy, Gregory; Morey, Rajendra A
    The amygdala is a major structure that orchestrates defensive reactions to environmental threats and is implicated in hypervigilance and symptoms of heightened arousal in posttraumatic stress disorder (PTSD). The basolateral and centromedial amygdala (CMA) complexes are functionally heterogeneous, with distinct roles in learning and expressing fear behaviors. PTSD differences in amygdala-complex function and functional connectivity with cortical and subcortical structures remain unclear. Recent military veterans with PTSD (n=20) and matched trauma-exposed controls (n=22) underwent a resting-state fMRI scan to measure task-free synchronous blood-oxygen level dependent activity. Whole-brain voxel-wise functional connectivity of basolateral and CMA seeds was compared between groups. The PTSD group had stronger functional connectivity of the basolateral amygdala (BLA) complex with the pregenual anterior cingulate cortex (ACC), dorsomedial prefrontal cortex, and dorsal ACC than the trauma-exposed control group (p<0.05; corrected). The trauma-exposed control group had stronger functional connectivity of the BLA complex with the left inferior frontal gyrus than the PTSD group (p<0.05; corrected). The CMA complex lacked connectivity differences between groups. We found PTSD modulates BLA complex connectivity with prefrontal cortical targets implicated in cognitive control of emotional information, which are central to explanations of core PTSD symptoms. PTSD differences in resting-state connectivity of BLA complex could be biasing processes in target regions that support behaviors central to prevailing laboratory models of PTSD such as associative fear learning. Further research is needed to investigate how differences in functional connectivity of amygdala complexes affect target regions that govern behavior, cognition, and affect in PTSD.
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    Brain circuits for the internal monitoring of movements.
    (Annu Rev Neurosci, 2008) Sommer, Marc A; Wurtz, Robert H
    Each 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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    Brain evolution by brain pathway duplication.
    (Philos Trans R Soc Lond B Biol Sci, 2015-12-19) Chakraborty, Mukta; Jarvis, Erich D
    Understanding the mechanisms of evolution of brain pathways for complex behaviours is still in its infancy. Making further advances requires a deeper understanding of brain homologies, novelties and analogies. It also requires an understanding of how adaptive genetic modifications lead to restructuring of the brain. Recent advances in genomic and molecular biology techniques applied to brain research have provided exciting insights into how complex behaviours are shaped by selection of novel brain pathways and functions of the nervous system. Here, we review and further develop some insights to a new hypothesis on one mechanism that may contribute to nervous system evolution, in particular by brain pathway duplication. Like gene duplication, we propose that whole brain pathways can duplicate and the duplicated pathway diverge to take on new functions. We suggest that one mechanism of brain pathway duplication could be through gene duplication, although other mechanisms are possible. We focus on brain pathways for vocal learning and spoken language in song-learning birds and humans as example systems. This view presents a new framework for future research in our understanding of brain evolution and novel behavioural traits.
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    Brain structural connectivity increases concurrent with functional improvement: evidence from diffusion tensor MRI in children with cerebral palsy during therapy.
    (NeuroImage. Clinical, 2015-01-09) Englander, Zoë A; Sun, Jessica; Laura Case; Mikati, Mohamad A; Kurtzberg, Joanne; Song, Allen W
    Cerebral Palsy (CP) refers to a heterogeneous group of permanent but non-progressive movement disorders caused by injury to the developing fetal or infant brain (Bax et al., 2005). Because of its serious long-term consequences, effective interventions that can help improve motor function, independence, and quality of life are critically needed. Our ongoing longitudinal clinical trial to treat children with CP is specifically designed to meet this challenge. To maximize the potential for functional improvement, all children in this trial received autologous cord blood transfusions (with order randomized with a placebo administration over 2 years) in conjunction with more standard physical and occupational therapies. As a part of this trial, magnetic resonance imaging (MRI) is used to improve our understanding of how these interventions affect brain development, and to develop biomarkers of treatment efficacy. In this report, diffusion tensor imaging (DTI) and subsequent brain connectome analyses were performed in a subset of children enrolled in the clinical trial (n = 17), who all exhibited positive but varying degrees of functional improvement over the first 2-year period of the study. Strong correlations between increases in white matter (WM) connectivity and functional improvement were demonstrated; however no significant relationships between either of these factors with the age of the child at time of enrollment were identified. Thus, our data indicate that increases in brain connectivity reflect improved functional abilities in children with CP. In future work, this potential biomarker can be used to help differentiate the underlying mechanisms of functional improvement, as well as to identify treatments that can best facilitate functional improvement upon un-blinding of the timing of autologous cord blood transfusions at the completion of this study.
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    Convergent transcriptional specializations in the brains of humans and song-learning birds.
    (Science, 2014-12-12) Pfenning, Andreas R; Hara, Erina; Whitney, Osceola; Rivas, Miriam V; Wang, Rui; Roulhac, Petra L; Howard, Jason T; Wirthlin, Morgan; Lovell, Peter V; Ganapathy, Ganeshkumar; Mouncastle, Jacquelyn; Moseley, M Arthur; Thompson, J Will; Soderblom, Erik J; Iriki, Atsushi; Kato, Masaki; Gilbert, M Thomas P; Zhang, Guojie; Bakken, Trygve; Bongaarts, Angie; Bernard, Amy; Lein, Ed; Mello, Claudio V; Hartemink, Alexander J; Jarvis, Erich D
    Song-learning birds and humans share independently evolved similarities in brain pathways for vocal learning that are essential for song and speech and are not found in most other species. Comparisons of brain transcriptomes of song-learning birds and humans relative to vocal nonlearners identified convergent gene expression specializations in specific song and speech brain regions of avian vocal learners and humans. The strongest shared profiles relate bird motor and striatal song-learning nuclei, respectively, with human laryngeal motor cortex and parts of the striatum that control speech production and learning. Most of the associated genes function in motor control and brain connectivity. Thus, convergent behavior and neural connectivity for a complex trait are associated with convergent specialized expression of multiple genes.
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    Corollary discharge across the animal kingdom.
    (Nat Rev Neurosci, 2008-08) Crapse, Trinity B; Sommer, Marc A
    Our movements can hinder our ability to sense the world. Movements can induce sensory input (for example, when you hit something) that is indistinguishable from the input that is caused by external agents (for example, when something hits you). It is critical for nervous systems to be able to differentiate between these two scenarios. A ubiquitous strategy is to route copies of movement commands to sensory structures. These signals, which are referred to as corollary discharge (CD), influence sensory processing in myriad ways. Here we review the CD circuits that have been uncovered by neurophysiological studies and suggest a functional taxonomic classification of CD across the animal kingdom. This broad understanding of CD circuits lays the groundwork for more challenging studies that combine neurophysiology and psychophysics to probe the role of CD in perception.
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    Cross-hemispheric collaboration and segregation associated with task difficulty as revealed by structural and functional connectivity.
    (J Neurosci, 2015-05-27) Davis, Simon W; Cabeza, Roberto
    Although it is known that brain regions in one hemisphere may interact very closely with their corresponding contralateral regions (collaboration) or operate relatively independent of them (segregation), the specific brain regions (where) and conditions (how) associated with collaboration or segregation are largely unknown. We investigated these issues using a split field-matching task in which participants matched the meaning of words or the visual features of faces presented to the same (unilateral) or to different (bilateral) visual fields. Matching difficulty was manipulated by varying the semantic similarity of words or the visual similarity of faces. We assessed the white matter using the fractional anisotropy (FA) measure provided by diffusion tensor imaging (DTI) and cross-hemispheric communication in terms of fMRI-based connectivity between homotopic pairs of cortical regions. For both perceptual and semantic matching, bilateral trials became faster than unilateral trials as difficulty increased (bilateral processing advantage, BPA). The study yielded three novel findings. First, whereas FA in anterior corpus callosum (genu) correlated with word-matching BPA, FA in posterior corpus callosum (splenium-occipital) correlated with face-matching BPA. Second, as matching difficulty intensified, cross-hemispheric functional connectivity (CFC) increased in domain-general frontopolar cortex (for both word and face matching) but decreased in domain-specific ventral temporal lobe regions (temporal pole for word matching and fusiform gyrus for face matching). Last, a mediation analysis linking DTI and fMRI data showed that CFC mediated the effect of callosal FA on BPA. These findings clarify the mechanisms by which the hemispheres interact to perform complex cognitive tasks.
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    Differential expression of glutamate receptors in avian neural pathways for learned vocalization.
    (J Comp Neurol, 2004-08-09) Wada, Kazuhiro; Sakaguchi, Hironobu; Jarvis, Erich D; Hagiwara, Masatoshi
    Learned vocalization, the substrate for human language, is a rare trait. It is found in three distantly related groups of birds-parrots, hummingbirds, and songbirds. These three groups contain cerebral vocal nuclei for learned vocalization not found in their more closely related vocal nonlearning relatives. Here, we cloned 21 receptor subunits/subtypes of all four glutamate receptor families (AMPA, kainate, NMDA, and metabotropic) and examined their expression in vocal nuclei of songbirds. We also examined expression of a subset of these receptors in vocal nuclei of hummingbirds and parrots, as well as in the brains of dove species as examples of close vocal nonlearning relatives. Among the 21 subunits/subtypes, 19 showed higher and/or lower prominent differential expression in songbird vocal nuclei relative to the surrounding brain subdivisions in which the vocal nuclei are located. This included relatively lower levels of all four AMPA subunits in lMAN, strikingly higher levels of the kainite subunit GluR5 in the robust nucleus of the arcopallium (RA), higher and lower levels respectively of the NMDA subunits NR2A and NR2B in most vocal nuclei and lower levels of the metabotropic group I subtypes (mGluR1 and -5) in most vocal nuclei and the group II subtype (mGluR2), showing a unique expression pattern of very low levels in RA and very high levels in HVC. The splice variants of AMPA subunits showed further differential expression in vocal nuclei. Some of the receptor subunits/subtypes also showed differential expression in hummingbird and parrot vocal nuclei. The magnitude of differential expression in vocal nuclei of all three vocal learners was unique compared with the smaller magnitude of differences found for nonvocal areas of vocal learners and vocal nonlearners. Our results suggest that evolution of vocal learning was accompanied by differential expression of a conserved gene family for synaptic transmission and plasticity in vocal nuclei. They also suggest that neural activity and signal transduction in vocal nuclei of vocal learners will be different relative to the surrounding brain areas.
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    Efficient coding of spatial information in the primate retina.
    (The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012-11) Doi, Eizaburo; Gauthier, Jeffrey L; Field, Greg D; Shlens, Jonathon; Sher, Alexander; Greschner, Martin; Machado, Timothy A; Jepson, Lauren H; Mathieson, Keith; Gunning, Deborah E; Litke, Alan M; Paninski, Liam; Chichilnisky, EJ; Simoncelli, Eero P
    Sensory neurons have been hypothesized to efficiently encode signals from the natural environment subject to resource constraints. The predictions of this efficient coding hypothesis regarding the spatial filtering properties of the visual system have been found consistent with human perception, but they have not been compared directly with neural responses. Here, we analyze the information that retinal ganglion cells transmit to the brain about the spatial information in natural images subject to three resource constraints: the number of retinal ganglion cells, their total response variances, and their total synaptic strengths. We derive a model that optimizes the transmitted information and compare it directly with measurements of complete functional connectivity between cone photoreceptors and the four major types of ganglion cells in the primate retina, obtained at single-cell resolution. We find that the ganglion cell population exhibited 80% efficiency in transmitting spatial information relative to the model. Both the retina and the model exhibited high redundancy (~30%) among ganglion cells of the same cell type. A novel and unique prediction of efficient coding, the relationships between projection patterns of individual cones to all ganglion cells, was consistent with the observed projection patterns in the retina. These results indicate a high level of efficiency with near-optimal redundancy in visual signaling by the retina.
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    Exploring the role of the substantia nigra pars reticulata in eye movements.
    (Neuroscience, 2011-12-15) Basso, MA; Sommer, MA
    Experiments that demonstrated a role for the substantia nigra in eye movements have played an important role in our understanding of the function of the basal ganglia in behavior more broadly. In this review we explore more recent experiments that extend the role of the substantia nigra pars reticulata from a simple gate for eye movements to include a role in cognitive processes for eye movements. We review recent evidence suggesting that basal ganglia nuclei beyond the substantia nigra may also play a role in eye movements and the cognitive events leading up to the production of eye movements. We close by pointing out some unresolved questions in our understanding of the relationship of basal ganglia nuclei and eye movements.
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    Functional connectivity in the retina at the resolution of photoreceptors.
    (Nature, 2010-10) Field, Greg D; Gauthier, Jeffrey L; Sher, Alexander; Greschner, Martin; Machado, Timothy A; Jepson, Lauren H; Shlens, Jonathon; Gunning, Deborah E; Mathieson, Keith; Dabrowski, Wladyslaw; Paninski, Liam; Litke, Alan M; Chichilnisky, EJ
    To understand a neural circuit requires knowledge of its connectivity. Here we report measurements of functional connectivity between the input and ouput layers of the macaque retina at single-cell resolution and the implications of these for colour vision. Multi-electrode technology was used to record simultaneously from complete populations of the retinal ganglion cell types (midget, parasol and small bistratified) that transmit high-resolution visual signals to the brain. Fine-grained visual stimulation was used to identify the location, type and strength of the functional input of each cone photoreceptor to each ganglion cell. The populations of ON and OFF midget and parasol cells each sampled the complete population of long- and middle-wavelength-sensitive cones. However, only OFF midget cells frequently received strong input from short-wavelength-sensitive cones. ON and OFF midget cells showed a small non-random tendency to selectively sample from either long- or middle-wavelength-sensitive cones to a degree not explained by clumping in the cone mosaic. These measurements reveal computations in a neural circuit at the elementary resolution of individual neurons.
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    Functional neuroimaging of emotionally intense autobiographical memories in post-traumatic stress disorder.
    (J Psychiatr Res, 2011-05) St Jacques, Peggy L; Botzung, Anne; Miles, Amanda; Rubin, David C
    Post-traumatic stress disorder (PTSD) affects regions that support autobiographical memory (AM) retrieval, such as the hippocampus, amygdala and ventral medial prefrontal cortex (PFC). However, it is not well understood how PTSD may impact the neural mechanisms of memory retrieval for the personal past. We used a generic cue method combined with parametric modulation analysis and functional MRI (fMRI) to investigate the neural mechanisms affected by PTSD symptoms during the retrieval of a large sample of emotionally intense AMs. There were three main results. First, the PTSD group showed greater recruitment of the amygdala/hippocampus during the construction of negative versus positive emotionally intense AMs, when compared to controls. Second, across both the construction and elaboration phases of retrieval the PTSD group showed greater recruitment of the ventral medial PFC for negatively intense memories, but less recruitment for positively intense memories. Third, the PTSD group showed greater functional coupling between the ventral medial PFC and the amygdala for negatively intense memories, but less coupling for positively intense memories. In sum, the fMRI data suggest that there was greater recruitment and coupling of emotional brain regions during the retrieval of negatively intense AMs in the PTSD group when compared to controls.
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    Induction of hippocampal long-term potentiation during waking leads to increased extrahippocampal zif-268 expression during ensuing rapid-eye-movement sleep.
    (J Neurosci, 2002-12-15) Ribeiro, Sidarta; Mello, Claudio V; Velho, Tarciso; Gardner, Timothy J; Jarvis, Erich D; Pavlides, Constantine
    Rapid-eye-movement (REM) sleep plays a key role in the consolidation of memories acquired during waking (WK). The search for mechanisms underlying that role has revealed significant correlations in the patterns of neuronal firing, regional blood flow, and expression of the activity-dependent gene zif-268 between WK and subsequent REM sleep. Zif-268 integrates a major calcium signal transduction pathway and is implicated by several lines of evidence in activity-dependent synaptic plasticity. Here we report that the induction of hippocampal long-term potentiation (LTP) during WK in rats leads to an upregulation of zif-268 gene expression in extrahippocampal regions during subsequent REM sleep episodes. This upregulation occurs predominantly in the amygdala, entorhinal, and auditory cerebral cortices during the first REM sleep episodes after LTP induction and reaches somatosensory and motor cerebral cortices as REM sleep recurs. We also show that hippocampal inactivation during REM sleep blocks extrahippocampal zif-268 upregulation, indicating that cortical and amygdalar zif-268 expression during REM sleep is under hippocampal control. Thus, expression of an activity-dependent gene involved in synaptic plasticity propagates gradually from the hippocampus to extrahippocampal regions as REM sleep recurs. These findings suggest that a progressive disengagement of the hippocampus and engagement of the cerebral cortex and amygdala occurs during REM sleep. They are also consistent with the view that REM sleep constitutes a privileged window for hippocampus-driven cortical activation, which may play an instructive role in the communication of memory traces from the hippocampus to the cerebral cortex.
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    Learned birdsong and the neurobiology of human language.
    (Ann N Y Acad Sci, 2004-06) Jarvis, Erich D
    Vocal learning, the substrate for human language, is a rare trait found to date in only three distantly related groups of mammals (humans, bats, and cetaceans) and three distantly related groups of birds (parrots, hummingbirds, and songbirds). Brain pathways for vocal learning have been studied in the three bird groups and in humans. Here I present a hypothesis on the relationships and evolution of brain pathways for vocal learning among birds and humans. The three vocal learning bird groups each appear to have seven similar but not identical cerebral vocal nuclei distributed into two vocal pathways, one posterior and one anterior. Humans also appear to have a posterior vocal pathway, which includes projections from the face motor cortex to brainstem vocal lower motor neurons, and an anterior vocal pathway, which includes a strip of premotor cortex, the anterior basal ganglia, and the anterior thalamus. These vocal pathways are not found in vocal non-learning birds or mammals, but are similar to brain pathways used for other types of learning. Thus, I argue that if vocal learning evolved independently among birds and humans, then it did so under strong genetic constraints of a pre-existing basic neural network of the vertebrate brain.