Disparate Brain Regions Research Articles

The subiculum: what it does, what it might do, and what neuroanatomy has yet to tell us

The subiculum is a pivotal but under-investigated structure positioned between the hippocampus proper and entorhinal and other cortices, as well as a range of subcortical structures. The subiculum has a range of electrophysiological and functional properties which are quite distinct from its input areas; given the widespread set of cortical and subcortical areas with which it interacts, it is able to influence activity in quite disparate brain regions. The rules governing plasticity of synaptic transmission in the hippocampal-subicular axis are poorly understood; this axis appears to share some properties in common with the hippocampus proper, but behaves quite differently in other respects. Equally, its functional properties are not well understood; it plays an important but ill-defined role in spatial navigation, mnemonic processing and control of the response to stress. Here, I review investigations of synaptic plasticity in the hippocampal-subicular pathway, recordings of subicular neurons in the freely moving behaving animal, the effects of behavioural and other stressors on subicular synaptic plasticity, and anatomical data on the dorso-ventral organization of the subiculum in relation to the hypothalamic-pituitary-adrenal (HPA) axis. I argue that there is a dorso-ventral segregation of function within the subiculum: the dorsal component appears principally concerned with the processing of information about space, movement and memory, whereas the ventral component appears to play a major regulatory role in the inhibition of the HPA axis.

Human Functional Neuroimaging Connectivity Research in Dependence

Functional and effective connectivity are relatively new techniques in the analysis of functional neuroimaging studies in humans. They have previously been used in studies of 'normal' psychological and neurological processes such as vision before gradually transferring into use in pathological disease states such as schizophrenia. These techniques are now beginning to extend into the field of substance misuse and dependence. So far, most functional neuroimaging studies in this field have shown consistent patterns of activation in several brain regions, and theories are emerging based upon these and animal models. Studies of brain connectivity can now begin to help further unravel the tangle of disparate brain regions and their connections that underpin the psychopharmacological processes of dependence.

Probing cortico-cortical interactions that underlie the multiple sensory, cognitive, and everyday functional deficits in schizophrenia

Schizophrenia patients exhibit impairments across multiple clinical, cognitive, and functional domains. A fundamental abnormality of the timing and/or efficiency of neural processes across disparate brain regions (i.e., cortico-cortical communications) may underlie many of the deficits in schizophrenia. Because gamma synchrony is temporally correlated with many cognitive processes, probing patterns of gamma activation may shed light on the functional integrity of neural circuits in schizophrenia and related disorders.

Gamma Oscillations Induced by Kainate Receptor Activation in the Entorhinal CortexIn Vitro

Gamma frequency (30-80 Hz) oscillations are recordable from human and rodent entorhinal cortex. A number of mechanisms used by neuronal networks to generate such oscillations in the hippocampus have been characterized. However, it is as yet unclear as to whether these mechanisms apply to other anatomically disparate brain regions. Here we show that the medial entorhinal cortex (mEC) in isolation in vitro generates gamma frequency oscillations in response to kainate receptor agonists. Oscillations had the same horizontal and laminar spatiotemporal distribution as seen in vivo and in the isolated whole-brain preparation. Oscillations occurred in the absence of input from the hippocampal formation and did not spread to lateral entorhinal regions. Pharmacological similarities existed between oscillations in the hippocampus and mEC in that the latter were also sensitive to GABAA receptor blockade, barbiturates, AMPA receptor blockade, and reduction in gap junctional conductance. Stellate and pyramidal neuron recordings revealed a large GABAergic input consisting of gamma frequency IPSP trains. Fast spiking interneurons in the superficial mEC generated action potentials at gamma frequencies phase locked to the local field. Stellate cells also demonstrated a subthreshold membrane potential oscillation at theta frequencies that was temporally correlated with a theta-frequency modulation in field gamma power. Disruption in this stellate theta frequency oscillation by the hyperpolarisation activated current (Ih) blocker ZD7288 also disrupted theta modulation of field gamma frequency oscillations. We propose that similar cellular and network mechanisms to those seen in the hippocampus generate and modulate persistent gamma oscillations in the entorhinal cortex.

Thoughts on the cerebellum as a model for cerebral cortical development and evolution.

This chapter explores the prospect of using the cerebellar cortex as a model for the development and evolution of the cerebral neocortex. At first, this would seem a nearly fruitless task given the readily apparent structural and functional differences between the two cortices. Cerebellum and cerebrum perform different associative tasks, the cellular 'circuit diagram' of the two structures is different, even the developmental sequences that give rise to the two structures differ markedly. Yet there are similarities between the structures at the conceptual level that are difficult to ignore. Both structures have a relatively simple modular circuitry and achieve their complexity by an increase in either the size or number of the modules. Both have massive commisures connecting the left and right halves of the structure. For the cortex this commisure is the obvious corpus callosum; the cerebellar commisure is made up of parallel fibres of the granule cells that pass freely across the midline. As they are thin and unmyelinated, the number of these crossing fibres may well exceed the number of the callosal axons by a significant amount. By far the most obvious similarity between cortex and cerebellum, however, is that they are both topologically sheet-like in structure. They are broad and wide in the two-dimensional plane of the pial membrane with a relatively modest thickness in the radial dimension. The question for this chapter then is whether these similarities, in particular the sheet-like organization are coincidental or indicative of larger themes that play deeper roles in the development and function of these two seemingly disparate brain regions.