Hippocampus - Wikipedia
Volumetric MRI analysis of the amygdala and the hippocampus in subjects with age-associated memory impairment: Correlation to visual and verbal memory. In contrast to the idea that hippocampal and amygdala volume loss occur in . were assessed using Spearman rank correlation coefficients. Effect of Hippocampal and Amygdala Connectivity on the Relationship Between Preschool Poverty and School-Age Depression. Article in.
They may precede clinically overt dementia by many years, or even decades Reiman et al. The appearance of these preclinical markers has been described as a highly ordered process summarized by Jack et al. Initially, very subtle morphological brain alterations were thought to become detectable in structural magnetic resonance imaging MRI only in later phases of neurodegeneration in preclinical AD, notably, a decrease in entorhinal cortex, hippocampal and amygdala volume Miller et al.
A recently published work on cognitively intact individuals Jack et al. Similar observations were reported by Edmonds indicating that neurodegeneration alone was 2.
The current investigation aims to extend the established findings of GM loss in the earliest stage of cognitive decline before MCI or even AD. We assessed of elderly individuals mean age, Based on neurocognitive follow-up at 18 months about half of controls remained cognitively stable sCONwhile the other half had subtle cognitive deteriorating control dCON. It is important to emphasize, that even the dCON participants at follow-up were still in the range of normal cognitive performance, yet with respect to the baseline assessment, these participants expressed first subtle cognitive deficits, clearly less pronounced to qualify for an MCI state.
We explored the patterns of GM loss in hippocampus and amygdala in these elderly controls displaying the first signs of cognitive decline as compared to stable controls as well as MCI cases as a second group of comparison. Materials and Methods Participants The protocol was approved by the ethics committee of the University Hospitals of Geneva. All experimental procedures were carried out in accordance with the approved guidelines and with the principles of the Declaration of Helsinki.
All participants were given written informed consent prior to inclusion. Participants were contacted via advertisements in local media to guarantee a community-based sample. An experienced neuropsychologist C. Those who met dementia DSM-IV diagnostic criteria on the basis of the neuropsychological and clinical assessments were excluded. Moreover, exclusion criteria included psychiatric or neurologic disorders, sustained head injury, history of major medical disorders neoplasm or cardiac illness.
Moreover, subjects were included if they had no alcohol or drug abuse, no regular use of neuroleptics, antidepressants or psychostimulants and no contraindications to MR imaging. To control for the confounding effect of cardiovascular diseases, individuals with subtle cardiovascular symptoms and a history of stroke and transient ischemic episodes were also excluded from the present study. The final sample included elderly individuals mean age, In the current study, we sought to examine the relationship between hippocampal volume and a commonly administered dementia-screening tool and a comprehensive cognitive battery in a cohort of 93 older adults without neurological injury, neurodegenerative disease or major psychiatric illness to: These measures are sub-divided into two composite cognitive scores comprising cognitive abilities that change with age fluid cognitive function or remain stable over time crystalized cognitive functions.
The delineation of a two-factor model a fluid factor and a crystalized factor instead of a single general intelligence factor is valuable when studying cognitive aging due to differences in the age curves of fluid and crystalized abilities Cattell, An extension of the two-factor, fluid and crystalized model, the Cattell-Horn-Carroll CHC theory of cognition extends the factors of general intelligence to nine broad abilities fluid reasoning, comprehension-knowledge, short-term memory, visual processing, auditory processing, long-term storage and retrieval, cognitive processing speed, quantitative knowledge and reading and writing; McGrew, In contrast, language-based cognitive abilities i.Amygdala and Hippocampus
In addition, we also predicted that smaller hippocampal volume would be associated with slower processing speed and poorer executive functions. These data would not only support the role of the hippocampus in cognition as shown in prior research on neurodegenerative disease and neurological disease states, but also extend these findings to cognitive aging.
Furthermore, these data would provide a strong foundation for development of predictive hippocampal biomarkers for future decline in longitudinal cohorts by characterizing cognitive aging in the hippocampus in the absence of neurological and neurodegenerative disease. Participants had a mean age of All participants provided written informed consent prior to enrollment.
Cognitive Aging and the Hippocampus in Older Adults
All study procedures were approved by the University of Florida Institutional Review Board prior to the start of the study.
Participants had the opportunity to ask the researchers any questions about study procedures prior to the start of the study.
No vulnerable populations were studied.
- Cognitive Aging and the Hippocampus in Older Adults
- Hippocampal and Amygdala Gray Matter Loss in Elderly Controls with Subtle Cognitive Decline
Exclusionary criteria included pre-existing neurological or psychiatric brain disorders, MRI contraindications such as metal or medical devices inside the body not approved to be scanned at 3Treported diagnosis of a neurodegenerative brain disease i. If damage to the hippocampus occurs in only one hemisphere, leaving the structure intact in the other hemisphere, the brain can retain near-normal memory functioning. Although the retrograde effect normally extends many years back before the brain damage, in some cases older memories remain.
This retention of older memories leads to the idea that consolidation over time involves the transfer of memories out of the hippocampus to other parts of the brain. This fact suggests that such abilities depend on different types of memory procedural memory and different brain regions.
Furthermore, amnesic patients frequently show "implicit" memory for experiences even in the absence of conscious knowledge.
For example, patients asked to guess which of two faces they have seen most recently may give the correct answer most of the time in spite of stating that they have never seen either of the faces before.
Some researchers distinguish between conscious recollection, which depends on the hippocampus, and familiarity, which depends on portions of the medial temporal lobe.
Place cell Image 6: Spatial firing patterns of 8 place cells recorded from the CA1 layer of a rat. The rat ran back and forth along an elevated track, stopping at each end to eat a small food reward. Dots indicate positions where action potentials were recorded, with color indicating which neuron emitted that action potential. Studies on freely moving rats and mice have shown many hippocampal neurons to act as place cells that cluster in place fields, and these fire bursts of action potentials when the animal passes through a particular location.
This place-related neural activity in the hippocampus has also been reported in monkeys that were moved around a room whilst in a restraint chair. Other cells in smaller proportion are inhibitory interneurons and these often show place-related variations in their firing rate which are much weaker.
There is little if any spatial topography in the representation; in general, cells lying next to each other in the hippocampus have uncorrelated spatial firing patterns.
Place cells are typically almost silent when a rat is moving around outside the place field but reach sustained rates as high as 40 Hzwhen the rat is near the center. Neural activity sampled from 30 to 40 randomly chosen place cells carries enough information to allow a rat's location to be reconstructed with high confidence. The size of place fields varies in a gradient along the length of the hippocampus, with cells at the dorsal end showing the smallest fields, cells near the center showing larger fields, and cells at the ventral tip showing fields that cover the entire environment.
They were undergoing an invasive procedure to localize the source of their seizureswith a view to surgical resection. The patients had diagnostic electrodes implanted in their hippocampus and then used a computer to move around in a virtual reality town. A study showed that the posterior part of the hippocampus is larger in these drivers than in the general public, and that a positive correlation exists between the length of time served as a driver and the increase in the volume of this part.
It was also found the total volume of the hippocampus was unchanged, as the increase seen in the posterior part was made at the expense of the anterior part, which showed a relative decrease in size. There have been no reported adverse effects from this disparity in hippocampal proportions.
The anterior part of the right hippocampus was larger and the posterior part was smaller, comparing with sighted individuals. Together these cells form a network that serves as spatial memory.
The first of such cells discovered in the s were the place cells, which led to the idea of the hippocampus acting to give a neural representation of the environment in a cognitive map. Getting lost is a common symptom of amnesia. These have been assigned as head direction cellsgrid cells and boundary cells.
Role in approach-avoidance conflict processing[ edit ] Further information: Reward system Approach-avoidance conflict happens when a situation is presented that can either be rewarding or punishing, and the ensuing decision-making has been associated with anxiety. Overall findings showed that the anterior hippocampus is sensitive to conflict, and that it may be part of a larger cortical and subcortical network seen to be important in decision making in uncertain conditions.
The Scientific World Journal
The authors suggest that a challenge is to understand how conflict processing relates to the functions of spatial navigation and memory and how all of these functions need not be mutually exclusive. Each plot shows 20 seconds of data, with a hippocampal EEG trace at the top, spike rasters from 40 simultaneously recorded CA1 pyramidal cells in the middle each raster line represents a different celland a plot of running speed at the bottom.
The top plot represents a time period during which the rat was actively searching for scattered food pellets. For the bottom plot the rat was asleep. The hippocampus shows two major "modes" of activity, each associated with a distinct pattern of neural population activity and waves of electrical activity as measured by an electroencephalogram EEG.
These modes are named after the EEG patterns associated with them: The main characteristics described below are for the rat, which is the animal most extensively studied. An active cell typically stays active for half a second to a few seconds. As the rat behaves, the active cells fall silent and new cells become active, but the overall percentage of active cells remains more or less constant.
In many situations, cell activity is determined largely by the spatial location of the animal, but other behavioral variables also clearly influence it.