301
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Amyloid Beta-Protein and Neural Network Dysfunction. JOURNAL OF NEURODEGENERATIVE DISEASES 2013; 2013:657470. [PMID: 26316994 PMCID: PMC4437331 DOI: 10.1155/2013/657470] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Accepted: 12/06/2012] [Indexed: 01/15/2023]
Abstract
Understanding the neural mechanisms underlying brain dysfunction induced by amyloid beta-protein (Aβ) represents one of the major challenges for Alzheimer's disease (AD) research. The most evident symptom of AD is a severe decline in cognition. Cognitive processes, as any other brain function, arise from the activity of specific cell assemblies of interconnected neurons that generate neural network dynamics based on their intrinsic and synaptic properties. Thus, the origin of Aβ-induced cognitive dysfunction, and possibly AD-related cognitive decline, must be found in specific alterations in properties of these cells and their consequences in neural network dynamics. The well-known relationship between AD and alterations in the activity of several neural networks is reflected in the slowing of the electroencephalographic (EEG) activity. Some features of the EEG slowing observed in AD, such as the diminished generation of different network oscillations, can be induced in vivo and in vitro upon Aβ application or by Aβ overproduction in transgenic models. This experimental approach offers the possibility to study the mechanisms involved in cognitive dysfunction produced by Aβ. This type of research may yield not only basic knowledge of neural network dysfunction associated with AD, but also novel options to treat this modern epidemic.
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302
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Watrous AJ, Tandon N, Conner CR, Pieters T, Ekstrom AD. Frequency-specific network connectivity increases underlie accurate spatiotemporal memory retrieval. Nat Neurosci 2013; 16:349-56. [PMID: 23354333 PMCID: PMC3581758 DOI: 10.1038/nn.3315] [Citation(s) in RCA: 204] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 12/19/2012] [Indexed: 11/17/2022]
Abstract
The medial temporal lobes, prefrontal cortex, and parts of parietal cortex form the neural underpinnings of episodic memory, which includes remembering both where and when an event occurred. Yet how these three key regions interact during retrieval of spatial and temporal context remains largely untested. Here, we employed simultaneous electrocorticographical recordings across multiple lobular regions, employing phase synchronization as a measure of network functional connectivity, while patients retrieved spatial and temporal context associated with an episode. Successful memory retrieval was characterized by greater global connectivity compared to incorrect retrieval, with the MTL acting as a convergence hub for these interactions. Spatial vs. temporal context retrieval resulted in prominent differences in both the spectral and temporal patterns of network interactions. These results emphasize dynamic network interactions as central to episodic memory retrieval, providing novel insight into how multiple contexts underlying a single event can be recreated within the same network.
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Affiliation(s)
- Andrew J Watrous
- Neuroscience Graduate Group, University of California, Davis, California, USA
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303
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Jacobson TK, Howe MD, Schmidt B, Hinman JR, Escabí MA, Markus EJ. Hippocampal theta, gamma, and theta-gamma coupling: effects of aging, environmental change, and cholinergic activation. J Neurophysiol 2013; 109:1852-65. [PMID: 23303862 DOI: 10.1152/jn.00409.2012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hippocampal theta and gamma oscillations coordinate the timing of multiple inputs to hippocampal neurons and have been linked to information processing and the dynamics of encoding and retrieval. One major influence on hippocampal rhythmicity is from cholinergic afferents. In both humans and rodents, aging is linked to impairments in hippocampus-dependent function along with degradation of cholinergic function. Cholinomimetics can reverse some age-related memory impairments and modulate oscillations in the hippocampus. Therefore, one would expect corresponding changes in these oscillations and possible rescue with the cholinomimetic physostigmine. Hippocampal activity was recorded while animals explored a familiar or a novel maze configuration. Reexposure to a familiar situation resulted in minimal aging effects or changes in theta or gamma oscillations. In contrast, exploration of a novel maze configuration increased theta power; this was greater in adult than old animals, although the deficit was reversed with physostigmine. In contrast to the theta results, the effects of novelty, age, and/or physostigmine on gamma were relatively weak. Unrelated to the behavioral situation were an age-related decrease in the degree of theta-gamma coupling and the fact that physostigmine lowered the frequency of theta in both adult and old animals. The results indicate that age-related changes in gamma and theta modulation of gamma, while reflecting aging changes in hippocampal circuitry, seem less related to aging changes in information processing. In contrast, the data support a role for theta and the cholinergic system in encoding and that hippocampal aging is related to impaired encoding of new information.
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Affiliation(s)
- Tara K Jacobson
- Dept. of Psychology, Behavioral Neuroscience, Univ. of Connecticut, Storrs, CT 06269, USA
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304
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Serruya MD, Sederberg PB, Kahana MJ. Power shifts track serial position and modulate encoding in human episodic memory. Cereb Cortex 2012; 24:403-13. [PMID: 23081881 DOI: 10.1093/cercor/bhs318] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The first events in a series exert a powerful influence on cognition and behavior in both humans and animals. This is known as the law of primacy. Here, we analyze the neural correlates of primacy in humans by analyzing electrocorticographic recordings in 84 neurosurgical patients as they studied and subsequently recalled lists of common words. We found that spectral power in the gamma frequency band (28-100 Hz) was elevated at the start of the list and gradually subsided, whereas lower frequency (2-8 Hz) delta and theta band power exhibited the opposite trend. This gradual shift in the power spectrum was found across a widespread network of brain regions. The degree to which the subsequent memory effect was modulated by list (serial) position was most pronounced in medial temporal lobe structures. These results suggest that globally increased gamma and decreased delta-theta spectral powers reflect a brain state that predisposes medial temporal lobe structures to enhance the encoding and maintenance of early list items.
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Affiliation(s)
- Mijail D Serruya
- Department of Neurology, Thomas Jefferson University, Philadelphia, PA 19107, USA
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305
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Nokia MS, Anderson ML, Shors TJ. Chemotherapy disrupts learning, neurogenesis and theta activity in the adult brain. Eur J Neurosci 2012; 36:3521-30. [PMID: 23039863 DOI: 10.1111/ejn.12007] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 07/26/2012] [Accepted: 08/30/2012] [Indexed: 12/24/2022]
Abstract
Chemotherapy, especially if prolonged, disrupts attention, working memory and speed of processing in humans. Most cancer drugs that cross the blood-brain barrier also decrease adult neurogenesis. Because new neurons are generated in the hippocampus, this decrease may contribute to the deficits in working memory and related thought processes. The neurophysiological mechanisms that underlie these deficits are generally unknown. A possible mediator is hippocampal oscillatory activity within the theta range (3-12 Hz). Theta activity predicts and promotes efficient learning in healthy animals and humans. Here, we hypothesised that chemotherapy disrupts learning via decreases in hippocampal adult neurogenesis and theta activity. Temozolomide was administered to adult male Sprague-Dawley rats in a cyclic manner for several weeks. Treatment was followed by training with different types of eyeblink classical conditioning, a form of associative learning. Chemotherapy reduced both neurogenesis and endogenous theta activity, as well as disrupted learning and related theta-band responses to the conditioned stimulus. The detrimental effects of temozolomide only occurred after several weeks of treatment, and only on a task that requires the association of events across a temporal gap and not during training with temporally overlapping stimuli. Chemotherapy did not disrupt the memory for previously learned associations, a memory independent of (new neurons in) the hippocampus. In conclusion, prolonged systemic chemotherapy is associated with a decrease in hippocampal adult neurogenesis and theta activity that may explain the selective deficits in processes of learning that describe the 'chemobrain'.
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Affiliation(s)
- Miriam S Nokia
- Department of Psychology, University of Jyvaskyla, PO Box 35, 40014 Jyvaskyla, Finland.
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306
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Spontaneously reactivated patterns in frontal and temporal lobe predict semantic clustering during memory search. J Neurosci 2012; 32:8871-8. [PMID: 22745488 DOI: 10.1523/jneurosci.5321-11.2012] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although it is well established that remembering an item will bring to mind memories of other semantically related items (Bousfield, 1953), the neural basis of this phenomenon is poorly understood. We studied how the similarity relations among items influence their retrieval by analyzing electrocorticographic recordings taken as 46 human neurosurgical patients studied and freely recalled lists of words. We first identified semantic components of neural activity that varied systematically with the meanings of each studied word, as defined by latent semantic analysis (Landauer and Dumais, 1997). We then examined the dynamics of these semantic components as participants attempted to recall the previously studied words. Our analyses revealed that the semantic components of neural activity were spontaneously reactivated during memory search, just before recall of the studied words. Further, the degree to which neural activity correlated with semantic similarity during recall predicted participants' tendencies to organize the sequences of their responses on the basis of semantic similarity. Thus, our work shows that differences in the neural correlates of semantic information, and how they are reactivated before recall, reveal how individuals organize and retrieve memories of words.
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307
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van Vugt MK, Sekuler R, Wilson HR, Kahana MJ. An electrophysiological signature of summed similarity in visual working memory. J Exp Psychol Gen 2012; 142:412-25. [PMID: 22963189 DOI: 10.1037/a0029759] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Summed-similarity models of short-term item recognition posit that participants base their judgments of an item's prior occurrence on that item's summed similarity to the ensemble of items on the remembered list. We examined the neural predictions of these models in 3 short-term recognition memory experiments using electrocorticographic/depth electrode recordings and scalp electroencephalography. On each experimental trial, participants judged whether a test face had been among a small set of recently studied faces. Consistent with summed-similarity theory, participants' tendency to endorse a test item increased as a function of its summed similarity to the items on the just-studied list. To characterize this behavioral effect of summed similarity, we successfully fit a summed-similarity model to individual participant data from each experiment. Using the parameters determined from fitting the summed-similarity model to the behavioral data, we examined the relation between summed similarity and brain activity. We found that 4-9 Hz theta activity in the medial temporal lobe and 2-4 Hz delta activity recorded from frontal and parietal cortices increased with summed similarity. These findings demonstrate direct neural correlates of the similarity computations that form the foundation of several major cognitive theories of human recognition memory.
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Affiliation(s)
- Marieke K van Vugt
- Department of Artificial Intelligence, University of Groningen, Groningen, the Netherlands.
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308
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Featherstone RE, Liang Y, Saunders JA, Tatard-Leitman VM, Ehrlichman RS, Siegel SJ. Subchronic ketamine treatment leads to permanent changes in EEG, cognition and the astrocytic glutamate transporter EAAT2 in mice. Neurobiol Dis 2012; 47:338-46. [DOI: 10.1016/j.nbd.2012.05.003] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2011] [Revised: 04/09/2012] [Accepted: 05/11/2012] [Indexed: 01/11/2023] Open
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309
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Cornwell BR, Arkin N, Overstreet C, Carver FW, Grillon C. Distinct contributions of human hippocampal theta to spatial cognition and anxiety. Hippocampus 2012; 22:1848-59. [PMID: 22467298 PMCID: PMC3390451 DOI: 10.1002/hipo.22019] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/01/2012] [Indexed: 11/06/2022]
Abstract
Current views of the hippocampus assign this structure, and its prominent theta rhythms, a key role in both cognition and affect. We studied this duality of function in humans, where no direct evidence exists. Whole-head magnetoencephalographic (MEG) data were recorded to measure theta activity while healthy participants (N = 25) navigated two virtual Morris water mazes, one in which they risked receiving aversive shocks without warning to induce anxiety and one in which they were safe from shocks. Results showed that threat of shock elevated anxiety level and enhanced navigation performance as compared to the safe condition. MEG source analyses revealed that improved navigation performance during threat was preferentially associated with increased left septal (posterior) hippocampal theta (specifically 4-8 Hz activity), replicating previous research that emphasizes a predominant role of the septal third of the hippocampus in spatial cognition. Moreover, increased self-reported anxiety during threat was preferentially associated with increased left temporal (anterior) hippocampal theta (specifically 2-6 Hz activity), consistent with this region's involvement in mediating conditioned and innate fear. Supporting contemporary theory, these findings highlight simultaneous involvement of the human hippocampus in spatial cognition and anxiety, and clarify their distinct correlates.
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Affiliation(s)
- Brian R Cornwell
- Section on Neurobiology of Fear and Anxiety, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892, USA.
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310
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Suthana N, Fried I. Percepts to recollections: insights from single neuron recordings in the human brain. Trends Cogn Sci 2012; 16:427-36. [PMID: 22795560 DOI: 10.1016/j.tics.2012.06.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 06/11/2012] [Accepted: 06/12/2012] [Indexed: 11/28/2022]
Abstract
Transformation of experience into memories that can guide future behavior is a common ability across species. However, only humans can declare their perceptions and memories of experienced events (episodes). The medial temporal lobe (MTL) is central to episodic memory, yet the neuronal code underlying the translation from sensory information to memory remains unclear. Recordings from neurons within the brain in patients who have electrodes implanted for clinical reasons provide an opportunity to bridge physiology with cognitive theories. Recent evidence illustrates several striking response properties of MTL neurons. Responses are selective yet invariant, associated with conscious perception, can be internally generated and modulated, and spontaneously retrieved. Representation of information by these neurons is highly explicit, suggesting abstraction of information for future conscious recall.
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Affiliation(s)
- Nanthia Suthana
- Department of Neurosurgery, David Geffen School of Medicine and Semel Institute For Neuroscience and Human Behavior, University of California, Los Angeles, CA, USA
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311
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Maturation of EEG oscillations in children with sodium channel mutations. Brain Dev 2012; 34:469-77. [PMID: 21940124 PMCID: PMC3278588 DOI: 10.1016/j.braindev.2011.08.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2011] [Revised: 08/27/2011] [Accepted: 08/29/2011] [Indexed: 11/21/2022]
Abstract
Dravet syndrome (DS) is a severe epileptic encephalopathy beginning in infancy in which children have difficult to control seizures and cognitive impairment. The majority of children with DS carry mutations of the gene Scn1a, which codes for the alpha subunit of the type 1 voltage-gated sodium channel and is important for the function of interneurons. Interneurons have a critical role in the generation of brain rhythms involved in cognitive processing. We hypothesized that children with DS with Scn1a mutations would have abnormal oscillatory activity. To address this hypothesis, we used EEG power spectral analysis during the wakening to determine if frequency and power are altered in 23 EEGs from 12 children with DS compared to 18 age-matched controls. While there were few differences between the EEG power spectra in DS and controls in children under 2years, in older children group differences were apparent. In DS children between 3 and 5years there were significant decreases in percentage of alpha power compared to controls and in DS children over age 6years there was a marked increase of theta and decrease of alpha compared to controls. Developmental status paralleled the power spectral analysis with an increasing likelihood of having severe cognitive problems with increasing age. These results demonstrate that Scn1a mutations result in an age-dependent alteration in oscillatory process. Such abnormalities in developmental progression of oscillations may play an important role in poor cognitive development in children with DS.
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312
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Ducharme G, Lowe GC, Goutagny R, Williams S. Early alterations in hippocampal circuitry and theta rhythm generation in a mouse model of prenatal infection: implications for schizophrenia. PLoS One 2012; 7:e29754. [PMID: 22238649 PMCID: PMC3253085 DOI: 10.1371/journal.pone.0029754] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Accepted: 12/05/2011] [Indexed: 11/20/2022] Open
Abstract
Post-mortem studies suggest that GABAergic neurotransmission is impaired in schizophrenia. However, it remains unclear if these changes occur early during development and how they impact overall network activity. To investigate this, we used a mouse model of prenatal infection with the viral mimic, polyriboinosinic–polyribocytidilic acid (poly I∶C), a model based on epidemiological evidence that an immune challenge during pregnancy increases the prevalence of schizophrenia in the offspring. We found that prenatal infection reduced the density of parvalbumin- but not somatostatin-positive interneurons in the CA1 area of the hippocampus and strongly reduced the strength of inhibition early during postnatal development. Furthermore, using an intact hippocampal preparation in vitro, we found reduced theta oscillation generated in the CA1 area. Taken together, these results suggest that redistribution in excitatory and inhibitory transmission locally in the CA1 is associated with a significant alteration in network function. Furthermore, given the role of theta rhythm in memory, our results demonstrate how a risk factor for schizophrenia can affect network function early in development that could contribute to cognitive deficits observed later in the disease.
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Affiliation(s)
- Guillaume Ducharme
- Douglas Mental Health University Institute, McGill University, Department of Psychiatry, Montréal, Québec, Canada
| | - Germaine C. Lowe
- Douglas Mental Health University Institute, McGill University, Department of Psychiatry, Montréal, Québec, Canada
| | - Romain Goutagny
- Douglas Mental Health University Institute, McGill University, Department of Psychiatry, Montréal, Québec, Canada
| | - Sylvain Williams
- Douglas Mental Health University Institute, McGill University, Department of Psychiatry, Montréal, Québec, Canada
- * E-mail:
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