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Electrocortical correlates of fixed-foreperiod decision tasks.Donald, Merlin , 1939- January 1968 (has links)
No description available.
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Electrocortical correlates of fixed-foreperiod decision tasks.Donald, Merlin , 1939- January 1968 (has links)
No description available.
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An investigation of the rat's perireticular nucleus and its possible role in the formation of corticofugal and corticopetal connectionsAdams, Niels C. January 1995 (has links)
No description available.
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Investigating the wire fraction of the neuropil in primate cerebral ortexJillani, Ngalla Edward 31 October 2011 (has links)
D. Phil., School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, 2011 / Whether the neuropil is a static, optimally wired entity, whose components must be
balanced in a certain way, is an open question. Are the proportions of the components
of the neuropil consistent across different mammalian cortices, especially in primates
where the cerebral cortex is complexly organized? This question is interesting
because the actual biological underpinnings of complex behaviours and intelligence in
big-brained primates remain enigmatic and why they seem qualitatively different from
other animals in terms of their cognitive abilities. Understanding changes that may
have occurred in the brain, especially at the level of neuropil organization, during the
evolution in primates is important to our growing understanding of the intellectual
abilities and behaviours exhibited by members of this group. The current series of
quantitative studies was aimed at investigating variations in the proportionality of the
“wire fraction” in three primate species, the olive baboon (Papio anubis), vervet
monkey (Cercopithecus aethiops) and the common chimpanzee (Pan troglodytes), in
a range of higher and lower order cortical areas, using a newly developed method that
involves standard and immunohistochemical staining techniques to reveal and
quantify the various profiles of the fine structures of the cerebral cortex. The results of
these studies demonstrate clear layer differences in the wire fraction of the cerebral
cortex, and for the most part, consistency in the neuropil wire fraction of the same
layer across areas of the cerebral cortex within and between individuals of the same
species; however, differences in the wire fraction of the neuropil were associated with
changes in brain size. It is apparent that the neuropil is not static, as wiring
“optimality” changes with layers and brain size and this has functional implications
regarding neuronal processing and behavioural outcomes. The adaptive rationale
adopted by evolutionary psychology studies to explain behaviours may be erroneous,
as adaptation does not always explain sufficiently the emergence of complex
behaviours related to brain size increases, especially in primates.
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Subcortical Inputs Governing Cortical Network ActivityConstantinople, Christine January 2013 (has links)
Sensory information is represented in cortex by cascades of excitation, the patterns of which are constrained and biased by anatomical connections between neurons. Additionally, in the living animal, functional connectivity is dynamically adjusted by internally generated background activity, which varies by arousal state and behavioral context. Therefore, to understand how excitation propagates through the cortex, it is necessary to characterize the laminar flow of signal propagation as well as spontaneous network activity, which will constrain that propagation. This thesis characterizes the nature and mechanisms of awake cortical network dynamics, as well as the sources of sensory inputs in different cortical layers of the rat somatosensory system. Mammalian brains generate internal activity independent of environmental stimuli. Internally generated states may bring about distinct cortical processing modes. To investigate how brain state impacts cortical circuitry, we recorded intracellularly from the same neurons, under anesthesia and subsequent wakefulness, in the rat barrel cortex. In every cell examined throughout layers 2-6, wakefulness produced a temporal pattern of synaptic inputs differing markedly from those under anesthesia. Recurring periods of synaptic quiescence, prominent under anesthesia, were abolished by wakefulness, which produced instead a persistently depolarized state. This switch in dynamics was unaffected by elimination of afferent synaptic input from thalamus, suggesting that arousal alters cortical dynamics by neuromodulators acting directly on cortex. Indeed, blockade of noradrenergic, but not cholinergic, pathways induced synaptic quiescence during wakefulness. This thesis shows that subcortical inputs from the locus coeruleus-noradrenergic system can switch local recurrent networks into different regimes via direct neuromodulation. Having characterized the nature of wakeful dynamics, I next sought to characterize how sensory information propagates through the cortex. The thalamocortical projection to layer 4 (L4) of primary sensory cortex is thought to be the main route by which information from sensory organs reaches the neocortex. Sensory information is believed to then propagate through the cortical column along the L4→L2/3→L5/6 pathway. This thesis shows that sensory-evoked responses of L5/6 neurons derive from direct thalamocortical synapses, rather than the intracortical pathway. A substantial proportion of L5/6 neurons exhibit sensory-evoked postsynaptic potentials and spikes with the same latencies as L4. Paired in vivo recordings from L5/6 neurons and thalamic neurons revealed significant convergence of direct thalamocortical synapses onto diverse types of infragranular neurons. Pharmacological inactivation of L4 had no effect on sensory-evoked synaptic input to L5/6 neurons, and responsive L5/6 neurons continued to discharge spikes. In contrast, inactivation of thalamus suppressed sensory-evoked responses. This thesis shows that L4 is not an obligatory distribution hub for cortical activity, contrary to long-standing belief, and that thalamus activates two separate, independent "strata" of cortex in parallel.
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Theoretical Investigation of NMDA Effect on the Cerebral CortexAL Saidi, Waleed Hamdan Khalfan January 2008 (has links)
This thesis examines the dynamical behaviour of incorporating NMDA (an excitatory neurotransmitter) for the electrodynamic model of the cerebral cortex. The model used is the mean-field model developed by Steyn-Ross et al. (2005) which describes the behaviour of the cortex in terms of parameters averaged over spatially localised populations. The behaviour of the model is determined by the four control parameters: inhibitory effect li, subcortical drive s, and NMDA neurotransmitter e ect set by an excitatory factor le and the magnesium concentration C. Adopting this model could give a better understanding of the cortex functionality and the anaesthetic mechanism. The model predicts that there are either one or three stationary states available to the cortex. We identify two of these with highly activated state and a quiescent state and focus on the transition between the two. Theoretical stability predictions (eigenvalue analysis) verified by a numerical simulation show that the system is unstable between the two Hopf bifurcations. In addition, in the stable region the steady states remains stable under a small perturbation, while in the unstable region either a transition between states or a limit cycle (oscillation) occurs depending on the position of the steady state.
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Gene expression in the mouse cerebellar cortexPopesco, Magdalena Cristina, January 2003 (has links)
Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xiii, 184 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Andrej Rotter, Dept. of Biochemistry. Includes bibliographical references (p. 158-184).
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Role of the posterior parietal cortex in multimodal spatial behavioursKwan, Teresa 11 1900 (has links)
The posterior parietal cortex (PPC) is a cortical region receiving inputs from different
sensory modalities which has been shown to subserve a visuospatial function. The
potential contribution of PPC in audiospatial behaviours and recognition of amodal spatial
correspondences were postulated and assessed in the present study. Adult male Long-
Evans rats received PPC lesions by aspiration, and they were compared to sham operated
control rats on three behavioural tasks. In the Morris water maze, the rats had to learn to
use the distal visual cues to locate an escape platform hidden in the pool. In an open field
task, the rats were assessed on their reactions to a spatial relocation of a visual or an
auditory object. In a spatial cross-modal transfer (CMT) task (Tees & Buhrmann, 1989),
rats were trained to respond to light signals using spatial rules, and were then subjected to
transfer tests using comparable sound signals. Results from the Morris water maze, the
open field, and the initial training phase of the spatial CMT task confirmed a visuospatial
deficit in PPC lesioned rats. However, if given sufficient training, PPC lesioned rats could
learn the location of a hidden platform in the Morris water maze, and they could also
acquire spatial rules in the CMT task. Such results indicated that the visuospatial deficits
in PPC lesioned rats were less severe than previously thought. On the other hand, a
persistent navigational difficulty characterized by a looping pattern of movement was
observed in the PPC lesioned rats in the Morris water maze. Results from the open field
indicated that PPC was less involved in audiospatial behaviours. Moreover, results also
indicated that PPC was not necessary for spatial CMT. Hence, data from the present
study did not support the idea that PPC played an essential role in supramodal spatial
abilities in the rats. Instead, data from the spatial CMT task seemed to imply a role of
PPC in managing conflicting spatial information coming from different sensory modalities.
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The effect of opiates on developing cerebral cortex : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy in Cell and Molecular Bioscience /Sargeant, Timothy John. January 2008 (has links)
Thesis (Ph.D.)--Victoria University of Wellington, 2008. / Includes bibliographical references.
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Speech sound coding and training-induced plasticity in primary auditory cortex /Engineer, Crystal Tasha, January 2008 (has links)
Thesis (Ph.D.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 105-106)
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