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Memory Encoding and Retrieval in the Aging Brain

David Friedman, Doreen Nessler and Ray Johnson, Jr.

ABSTRACT

Decline in episodic memory, the encoding and retrieval of autobiographical events, is a hallmark of normal cognitive aging. Although the primary causes of this decline remain elusive, event-related brain potential (ERP) studies have contributed to an understanding of age-related episodic memory failure. These data reveal that, although the retrieval-based episodic memory (EM) effect does not differ dramatically between young and older adults, the acquisition-related data suggest a decline in episodic encoding (i.e., semantic elaboration) with increasing age. We conclude that, at the current state of knowledge, encoding deficiencies are more important than retrieval deficits in understanding the causes of episodic memory decline in the older adult.

From Amnesia to Dementia: ERP Studies of Memory and Language

Jason R. Taylor and John M. Olichney

ABSTRACT

Cognitive event-related potential (ERP) studies of memory and language impairments in amnesia and Alzheimer’s disease (AD) are reviewed. Well-circumscribed lesions of the medial temporal lobe (MTL) or diencephalon causing an amnestic syndrome, an inability to encode and retrieve episodic memories beyond the brief duration of working memory, appear to produce altered plasticity of the late positive P600 component, but usually spare P300 and N400 components. The neuropathology of AD affects MTL and extends to neocortical association areas, causing deficits of episodic and semantic memory. In AD dementia, the P300, N400, and P600 all commonly show abnormalities. ERP studies of individuals with mild cognitive impairment may reveal neurophysiological changes prior to the emergence of clinical deficits, which could advance the early detection and diagnosis of AD.

Visual Memory Deficits in Temporal Lobe Epilepsy: Toward a Multifactorial Approach

M. Vannucci

ABSTRACT

Temporal lobe epilepsies (TLE) are associated with material-specific memory deficits depending on the side of seizure origin. However, while verbal memory deficits have been consistently reported in patients with left-sided TLE, the relationship between visual memory deficits and right-sided TLE is more complex. Here, we review factors that influence the pattern of lateralization and the nature of visual memory impairments in TLE and discuss the possible relationship between these deficits and perceptual impairments in TLE patients.

Event-Related Potentials in Psychiatry

Oliver Pogarell, Christoph Mulert and Ulrich Hegerl

ABSTRACT

Electrophysiological assessments of psychiatric disorders have produced a number of promising, highly replicable findings and thus carry the potential of becoming clinically utilizable in the diagnostic or prognostic evaluation of psychopathological conditions. The procedures involved are rather complex technically and the interpretation of the findings require a combined neurophysiological and clinical expertise. On the other hand, electrophysiological techniques are in general non-invasive and relatively inexpensive, and neurophysiology laboratories are widely available in the clinical setting.

Among these techniques, event-related potentials (ERPs) are of major interest in psychiatry, particularly since these tools can indicate cortical neuronal dysfunctions, which play a major role in various neuropsychiatric disorders.

Spatial-Temporal Current Source Correlations and Cortical Connectivity

R. W. Thatcher, C. J. Biver and D. North

ABSTRACT

The purpose of this study was to explore spatial-temporal correlations between 3-dimensional current density estimates using Low Resolution Electromagnetic Tomography (LORETA).

The electroencephalogram (EEG) was recorded from 19 scalp locations from 97 subjects. LORETA current density was computed for 2,394 gray matter pixels. The gray matter pixels were grouped into 33 left hemisphere and 33 right hemisphere regions of interest (ROIs) based on groupings of Brodmann areas. The average source current density in a given region of interest (ROI) was computed for each 2 second epoch of EEG and then a Pearson product correlation coefficient was computed over the time series of successive 2 second epochs of current density between all pairwise combinations of ROIs during the resting eyes-closed EEG session.

Rhythmic changes in source correlation as a function of distance were present in all regions of interest. Also, maximum correlations at certain frequencies were present independent of distance. The occipital regions exhibited the highest short distance correlations and the frontal regions exhibited the highest long distance correlations. In general, the right hemisphere exhibited higher intra-hemispheric source correlations than the left hemisphere especially in the temporal, parietal and occipital cortex. The strongest left vs. right hemisphere differences were in the alpha frequency band (8-12 Hz) and in the gamma frequency band (37-40 Hz).

The pattern of spatial frequencies in different cortical lobules is consistent with differences in neural packing density and the operation of ‘U’ shaped fiber systems. The general conclusions were: 1- the higher the packing density then the greater the intra-cortical connection contribution to LORETA source correlations, 2- spatial frequencies are primarily due to intra-cortical ‘U’ shaped fiber connections and long distance fiber connections, 3- posterior and temporal cortical intra-hemispheric coupling is generally stronger in the right hemisphere than in the left hemisphere.

Visual Completion Processing in Human Face Perception

Xiang-Li Chu, Yin-Hua Wang and Yu-Ping Wang

ABSTRACT

Subjects discriminated whether two sequentially presented human face pictures (S1 and S2) were identical while event-related potentials were recorded to explore the neural basis of visual completion for occluded objects. Four kinds of stimulus trials were employed: S2 and S1 were identical (match-complete); S2 and S1 were identical, but S2 was partially occluded (match-incomplete); S2 was a different face from S1 (mismatch-complete); S2 was different from S1, and was partially occluded (mismatch-incomplete). Incomplete faces enhanced the amplitude of N1 compared with complete faces. The peak latency of N2 elicited by incomplete faces was delayed about 20 ms compared with complete faces. The enhancement of N1 is related to visual completion processing that requires additional time.

Considerations of the Ischemic Basis and Therapy of Alzheimer Disease

E. Niedermeyer

ABSTRACT

A recently presented concept of Alzheimer disease (AD) is based on a primarily ischemic (rather than degenerative) type of brain disease. Etiologically, this new concept is presumed to be related to the human upright gait along with individual predisposition.
The proposed treatment — head-down therapy (HDT) — is the centerpoint of this presentation: a simple and generally accessible type of therapy, with monitoring by neuropsychological questioning, electroencephalography, and transcranial Doppler. As a treatment of AD (limited to stage 1), HDT is expected to be helpful. It is possible, however, that its prophylactic use may be of even greater importance.

Transcranial and Deep Brain Stimulation Approaches as Treatment for Depression

Anne Rau, Nicola Großheinrich, Ulrich Palm, Oliver Pogarell and Frank Padberg

ABSTRACT

Given that a considerable portion of depressed patients does not respond to or remit during pharmacotherapy, there is increasing interest in non-pharmacological strategies to treat depressive disorders. Several brain stimulation approaches are currently being investigated as novel therapeutic interventions beside electroconvulsive therapy (ECT), a prototypic method in this field with proven effectiveness. These neurostimulation methods include repetitive transcranial magnetic stimulation (rTMS), magnetic seizure therapy (MST), vagus nerve stimulation (VNS), deep brain stimulation (DBS) and transcranial direct current stimulation (tDCS). It is via different neuroanatomically defined “windows” that the various approaches access the neuronal networks showing an altered function in depression. Also, the methods vary regarding their degree of invasiveness. One or the other method may finally achieve antidepressant effectiveness with minimized side effects and constitute a new effective treatment for major depression.

Nonconvulsive Status Epilepticus Causing Prolonged Stupor After Intraventricular Hemorrhage: Report of a Case

J. L. Fernández-Torre, Z. Agirre, R. Puchades, E. Marco De Lucas and A. Oterino

ABSTRACT

We describe the case of an octogenarian woman who experienced a severe alteration of mental state due to nonconvulsive status epilepticus (NCSE) complicating an intraventricular hemorrhage. Our report emphasizes that NCSE may be the cause of unexplained neurological deterioration in elderly patients with acute brain injury.