Mediotemporal Lobe: Research reports

Mediotemporal lobe

November 2003

Questioning the medial temporal lobe

The medial temporal lobe includes the hippocampus, the amygdala, and the entorhinal and perirhinal cortices. It is often talked about as a single unit, but recently a prominent neurobiologist has questioned this usage. For one thing, the region didn’t evolve as one unit — the different regions arose at different times during primate evolution. Therefore, can it really be an integrated system with a common function? Her work with rhesus monkeys suggests rather that these different parts may serve cooperative and even competitive functions.
http://gateways.bmn.com/conferences/list/view?rp=2003-SFN-4-S3 (BioMedNet: free registration required)

Magnetic resonance imaging may help predict future memory decline

A six-year imaging study of 45 healthy seniors assessed changes in brain scans against cognitive decline. They found that progressive atrophy in the medial temporal lobe was the most significant predictor of cognitive decline, which occurred in 29% of the subjects.
The study appeared in the December issue of Radiology. Full reference
http://www.eurekalert.org/pub_releases/2003-11/rson-mhr111703.htm

March 2003

Activity in the mediotemporal lobe lower in elderly with poor memory

An imaging study has revealed that, although there is no difference on standard MRI scans,scans showing the amount of oxygen (and thus activity) find that elderly persons with a poor memory have less activity in the mediotemporal lobe when storing new information than elderly persons with a normally functioning memory.This more sensitive scan may help early diagnosis of Alzheimer's. You can see an image of the brain scans at www.nwo.nl/news.
The research was done as part of a doctoral thesis by Dr Sander Daselaar.
http://www.eurekalert.org/pub_releases/2003-03/nofs-svp032103.htm
http://www.nwo.nl/NWOHome.nsf/pages/NWOP_5KRH7V?OpenDocument&g=NWO&n=ACPP_4WMESE&rc=1

November 2001

Imaging study confirms role of medial temporal lobe in memory consolidation

Lesions in the medial temporal lobe (MTL) typically produce amnesia characterized by the disproportionate loss of recently acquired memories. Such memory loss has been interpreted as evidence for a memory consolidation process guided by the MTL. A recent imaging study confirms this view by showing temporally graded changes in MTL activity in healthy older adults taking a famous faces remote memory test. Evidence for such temporally graded change in the hippocampal formation was mixed, suggesting it may participate only in consolidation processes lasting a few years. The entorhinal cortex (also part of the MTL) was associated with temporally graded changes extending up to 20 years, suggesting that it is the entorhinal cortex, rather than the hippocampal formation, that participates in memory consolidation over decades. The entorhinal cortex is damaged in the early stages of Alzheimer’s disease (AD).
The report appeared in Nature neuroscience. Full reference
http://www.nature.com/neurolink/v4/n11/abs/nn739.html

Competition between memory systems

Learning and memory in humans rely upon several memory systems. For example, the medial temporal lobe (MTL) is associated with declarative learning (facts and events). The basal ganglia is associated with nondeclarative learning (learning you derive from experience, that may not be conscious). A recent imaging study looked at how these memory systems interact during classification learning. During the nondeclarative learning task, there was an increase in activity in the basal ganglia, and a decrease in activity in the MTL. During the memorization task (testing declarative learning), the reverse was true. Further examination found rapid modulation of activity in these regions at the beginning of learning, suggesting that subjects relied upon the medial temporal lobe early in learning. However, this dependence rapidly declined with training.
The report appeared in the 29 November issue of Nature. Full reference
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v414/n6863/abs/414546a0_fs.html
http://www.eurekalert.org/pub_releases/2001-11/mgh-isi112601.htm

Hippocampus

February 2004

More light shed on memory encoding

Anything we perceive contains a huge amount of sensory information. How do we decide what bits to process? New research has identified brain cells that streamline and simplify sensory information, markedly reducing the brain's workload. The study found that when monkeys were taught to remember clip art pictures, their brains reduced the level of detail by sorting the pictures into categories for recall, such as images that contained "people," "buildings," "flowers," and "animals." The categorizing cells were found in the hippocampus. As humans do, different monkeys categorized items in different ways, selectingdifferent aspects of the same stimulus image, most likely reflectingdifferent histories, strategies, and expectations residing within individual hippocampal networks.
The findings are reported in the March 2 issue of the Proceedings of the National Academy of Sciences. Full reference
http://www.eurekalert.org/pub_releases/2004-02/wfub-nfo022604.htm

Now definite? Memories are consolidated during sleep

Researchers of a new study claim that their research finally settles the question of whether or not sleep consolidates new memories. The study involved detailed recording of specific learning- and memory- related areas (hippocampus and forebrain) in the brains of rats. The rats were exposed to four kinds of novel objects. Analysis of brain signals before, during, and after this experience, revealed "reverberations" of distinctive brain wave patterns across all the areas being monitored for up to 48 hours after the novel experience. This pattern was much more prevalent in slow-wave sleep than in REM sleep. Previous studies by the same researchers have found that the activation of genes that affect memory consolidation occurs during REM sleep, not slow-wave sleep. It is proposed that both stages of sleep are important for memory consolidation. Previous studies have tended to focus solely on the hippocampus, and have observed brain activity for a much shorter period.
The researchers published their findings on Jan. 19, 2004, in the online Public Library of Science. Full reference
http://www.eurekalert.org/pub_releases/2004-01/dumc-etm011304.htm
http://www.eurekalert.org/pub_releases/2004-01/plos-brd011204.htm
http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371/journal.pbio.0020037
Full text: http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371%2Fjournal.pbio.0020024

Exercise may counteract bad effect of high-fat diet on memory

An animal study has investigated the interaction of diet and exercise on synaptic plasticity (an important factor in learning performance). A diet high in fat reduced levels of brain-derived neurotrophic factor (BDNF) in the hippocampus, and impaired performance on spatial learning tasks, but both of these consequences were prevented in those animals with access to voluntary wheel-running. Exercise appeared to interact with the same molecular systems disrupted by the high-fat diet.
The study appeared in Neuroscience. Full reference
http://journals.bmn.com/jsearch/search/record?uid=NSC.bmn09190_03064522_v0123i02_03007425&rendertype=abstract

Forgetting may sometimes be an active process

New evidence suggests that forgetting may not simply be the passive phenomenon it has always been thought. Rather than simply a failure to properly encode or consolidate memories, forgetting may also be an active process — a deliberate action to erase unwanted memories. The recent study involved seeing the effect of a memory-blocking drug called APV on slices of brain tissue taken from the hippocampus of rats. APV blocks receptors for the neurotransmitter NMDA, which mediates the strengthening of synapses. While, as expected, NMDA activity was reduced in the treated hippocampal neurons, it was also found that “sharp waves” doubled in magnitude. This type of electrical activity is little understood, but it is known that such waves occur when an animal is alert but not actively exploring its environment or receiving sensory input, and they do not occur when brain activity associated with memory processing is occurring. Thus, the fact that a drug known to block memory, enhances sharp waves, is suggestive. The researchers speculate that sharp waves might work by reversing long-term potentiation — the mechanism by which synapses are thought to be strengthened — and that their function is to erase some of the information that was encoded during the active phase.
http://gateways.bmn.com/neuroscience/news?uid=NEWS.040114-1

More evidence for active forgetting

In an imaging study involving 24 people aged 19 to 31, participants were given pairs of words and told to remember some of the matched pairs but forget others. Trying to shut out memory appeared more demanding than remembering, in that some areas of the brain were significantly more when trying to suppress memory. Both the prefrontal cortex and the hippocampus were active. Those whose prefrontal cortex and hippocampus were most active during this time were most successful at suppressing memory.
The study appeared in the January 9 issue of Science. Full reference
http://www.eurekalert.org/pub_releases/2004-01/su-rrb010604.htm

Gene essential for development of normal brain connections discovered

After birth, learning and experience change the architecture of the brain dramatically. The structure of individual neurons, or nerve cells, changes during learning to accommodate new connections between neurons. Neuroscientists believe these structural changes are initiated when neurons are activated, causing calcium ions to flow into cells and alter the activity of genes. Now the first gene, CREST, known to mediate these changes in the structure of neurons in response to calcium, has been discovered. In the study, it was found that mice lacking this gene didn’t develop normally in response to sensory experience, and their brains, while normal at birth, later showed far less interconnectivity between neurons. The gene produces a protein that, in adult humans, is produced in the hippocampus. It is therefore speculated that the protein may be necessary for learning and memory storage. The discovery of this gene may have implications for certain types of learning disorders in humans.
The paper featured on the cover of the January 9 issue of Science. Full reference
http://www.eurekalert.org/pub_releases/2004-01/uoc--gef010804.htm

Brain protein affecting learning and memory discovered

A significant new brain protein has been identified. Cypin is found throughout the body, but in the brain it now appears that it regulates neuron branching in the hippocampus. Such branching is thought to increase when learning occurs, and a reduction in branching is associated with certain neurological diseases. Discovery of this protein opens the possibility of new drug therapies for treating neurological disorders, and perhaps even memory-enhancing drugs.
The paper was published online 18 January, and appeared in the February issue of Nature Neuroscience. Full reference
http://www.eurekalert.org/pub_releases/2004-01/rtsu-rsd011204.htm
http://news.independent.co.uk/world/science_medical/story.jsp?story=482567

More learned about how spatial navigation works in humans

Researchers monitored signals from individual brain cells as patients played a computer game in which they drove around a virtual town in a taxi, searching for passengers who appeared in random locations and delivering them to their destinations. Previous research has found specific cells in the brains of rodents that respond to “place”, but until now we haven’t known whether humans have such specific cells. This study identifies place cells (primarily found in the hippocampus), as well as “view” cells (responsive to landmarks; found mainly in the parahippocampal region) and “goal” cells (responsive to goals, found throughout the frontal and temporal lobes). Some cells respond to combinations of place, view and goal — for example, cells that responded to viewing an object only when that object was a goal.
The study was published in the Sept. 11 edition of Nature. Full reference
http://www.eurekalert.org/pub_releases/2003-09/uoc--vgu091003.htm

Another step in understanding how memories are formed

The electrical activity of individual neurons in the brains of two adult rhesus monkeys was monitored while the monkeys played a memory-based video game in which an image pops up on the computer screen with four targets—white dots—superimposed on it. The monkeys’ task was to learn which target on which image was associated with a reward (a drop of their favorite fruit juice). Dramatic changes in the activity of some hippocampal neurons, which the scientists called "changing cells", paralleled their learning, indicating that these neurons are involved in the initial formation of new associative memories. In some of the cells, activity continued after the animal had learned the association, suggesting that these cells may participate in the eventual storage of the associations in long-term memory.
The findings are reported in the June 6 issue of Science. Full reference
http://www.eurekalert.org/pub_releases/2003-06/nyu-fir060503.htm
http://tinyurl.com/ftob

Brain implant may restore memory

An artificial hippocampus — a programmed silicone chip — is to be linked with live tissue taken from rat brains, and then will be tested on live animals. If all goes well, it will then be tested as a way to help people who have suffered brain damage due to stroke, epilepsy or Alzheimer's disease.
http://www.guardian.co.uk/international/story/0,3604,912940,00.html
http://www.newscientist.com/news/news.jsp?id=ns99993488
http://www.eurekalert.org/pub_releases/2003-03/ns-twf031203.htm

Another step in understanding how sleep affects memory

The value of sleep for memory takes a further step in being understood in new rodent research, which found that, as the rodents slept, the thalamus at the base of their brains originated bursts of electrical activity (“sleep spindles”), which were then detected in the somatosensory neocortex. Some 50 msec later, the hippocampus responded with a pulse of electricity (a “ripple”). "This neocortical-hippocampal dialogue may provide a selection mechanism for the time-compressed replay of information learned during the day." It’s suggested that the ripple is the hippocampus sending back neat, compact waves of memory to the neocortex where they are filed away for future reference. Most of this activity took place during slow wave sleep, the stage which makes up the majority of the sleep cycle.
The paper was published in the February 18 issue of Proceedings of the National Academy of Sciences. Full reference

Gene linked to poor episodic memory

Brain derived neurotrophic factor (BDNF) plays a key role in neuron growth and survival and, it now appears, memory. We inherit two copies of the BDNF gene - one from each parent - in either of two versions. Slightly more than a third inherit at least one copy of a version nicknamed "met," which the researchers have now linked to poorer memory. Those who inherit the “met” gene appear significantly worse at remembering events that have happened to them, probably as a result of the gene’s effect on hippocampal function. Most notably, those who had two copies of the “met” gene scored only 40% on a test of episodic (event) memory, while those who had two copies of the other version scored 70%. Other types of memory did not appear to be affected. It is speculated that having the “met” gene might also increase the risk of disorders such as Alzheimer’s and Parkinsons.
The study was reported in the January 24 issue of Cell. Full reference
http://www.nih.gov/news/pr/jan2003/nimh-23.htm
http://www.eurekalert.org/pub_releases/2003-01/niom-hga012203.htm
http://news.bbc.co.uk/1/hi/health/2687267.stm

More details about how memories are formed in the hippocampus

We know how important the hippocampus is in forming memories, but now, using newly developed imaging techniques, researchers have managed to observe how activity patterns within specific substructures of the hippocampus change during learning. The study identified areas within the hippocampus (the cornu ammonis and the dentate gyrus) as highly active during encoding of face-name pairs. This activity decreased as the associations were learned. A different area of the hippocampus (the subiculum) was active primarily during the retrieval of the face-name associations. Activity in the subiculum also decreased as retrieval became more practiced.
The report appeared in the Jan. 24 edition of Science. Full reference
http://www.eurekalert.org/pub_releases/2003-01/uoc--som012303.htm

May 2002

Brain region involved in recalling memories from smell identified

We all know the power of smell in triggering the recall of memories. New research has found the specific area of the brain involved in this process - a section of the hippocampus called CA3. The hippocampus has long been known to play a crucial part in forming new memories. It appears that the CA3 region of the hippocampus is crucial for recalling memories from partial representations of the original stimulus.
The findings appeared in the July 12 issue of Science. Full reference
http://www.eurekalert.org/pub_releases/2002-05/bcom-tr052902.htm
http://news.bbc.co.uk/hi/english/health/newsid_2017000/2017321.stm

December 2001

Rhythm rather than strength of neural activity may be crucial for memory formation

The strength of the electrical activity between neurons has long been thought to be the critical factor in forming memories, but new research suggests that at least in two critical brain areas, memory may hinge more on the timing than on the strength of neural activity. It seems that, as subjects studied word lists, clusters of neurons in the rhinal cortex and the hippocampus—adjacent brain areas already implicated in memory—fired synchronized electrical bursts that paved the way for remembering those words later. Moreover, the coordination of cell activity in the same two brain regions plummetted for a fraction of a second just after participants remembered a word from the list, possibly signaling an end to a coordinated neural effort. "Memory may emerge when rhinal and hippocampal neurons synchronously oscillate and then desynchronize."
The report is due to appear in the December issue of Nature Neuroscience. Full reference
http://www.sciencenews.org/20011110/fob6.asp
http://news.bmn.com/news/story?day=011105&story=1

New study contradicts earlier finding of new brain cell growth in the adult primate neocortex

A very exciting finding a couple of years ago, was that adult monkeys were found to be able to create new neurons in the neocortex, the most recently evolved part of the brain. However a new study, using the most sophisticated cell analysis techniques available to analyze thousands of cells in the neocortex, has found that those neurons that appear to be new are in fact two separate cells, usually one “old” neuron and one newly created cell of a different type, such as a glial cell — although new neurons were indeed found in the hippocampus and the olfactory bulb (both older parts of the brain).
The report appeared in the Dec. 7 issue of the journal Science. Full reference
http://www.eurekalert.org/pub_releases/2001-12/uorm-std120601.htm

Amygdala

August 2003

Key brain link in associative learning directly observed

Rat studies have now shown that the amygdala supports the formation of new associations by changing nerve cell firing patterns in a different but connected part of the brain. In earlier studies, the researchers had demonstrated that nerve cells in the amygdala and the orbitofrontal cortex changed their firing patterns to reflect new associations between cues and outcomes. In this later study, they examined how changes in neural activity in amygdala might be supporting changes in the orbitofrontal cortex. Rats were first deprived of water, then repeatedly given either desirable drinking water, laced with sugar, or undesirable drinking water, laced with quinine. The associations then learned would show up in the orbitofrontal cortex when the rats smelled the odor cue. The same activation patterns did not however, show up in those rats who had their amygdala chemically lesioned (although these rats still learned to avoid the undesirable drinking water). Specifically, although lesioned rats had neurons in the orbitofrontal cortex that were responsive to the odor cues, they did not have neurons that were responsive in anticipation of the predicted outcome. The responsive neurons were also less associative, more responsive to the identity of the cue rather than the association betwen odor and consequence.
The study was published in the August 28 issue of Neuron. Full reference
http://www.eurekalert.org/pub_releases/2003-08/jhu-kbl082803.htm

April 2002

Fear-conditioning study demonstrates long-suspected link between longterm potentiation and learning

It has long been felt that learning and memory must require physical changes in neurons that increase their responsivity to other neurons, so that they will continue to respond in the long-term even in the absence of external stimuli. Until now, however, noone has been able to actually demonstrate that this long-term potentiation occurs during learning. A new direction has proved to be more successful. Investigation of changes in the amygdala (a part of the brain associated with emotional response) after rats had been trained to fear a sound, found that postsynaptic neurons in the amygdala failed to produce any noticeable increase in electrical current, suggesting they had already been potentiated by their presynaptic partners.
The study was reported in April 11 issue of Neuron. Full reference

May 2001

Amygdala may be critical for allowing perception of emotionally significant events despite inattention

We choose what to pay attention to, what to remember. We give more weight to some things than others. Our perceptions and memories of events are influenced by our preconceptions, and by our moods. Researchers at Yale and New York University have recently published research indicating that the part of the brain known as the amygdala is responsible for the influence of emotion on perception. This builds on previous research showing that the amygdala is critically involved in computing the emotional significance of events. The amygdala is connected to those brain regions dealing with sensory experiences, and the theory that these connections allow the amygdala to influence early perceptual processing is supported by this research. Dr. Anderson suggests that “the amygdala appears to be critical for the emotional tuning of perceptual experience, allowing perception of emotionally significant events to occur despite inattention.”
The study is reported in the May 17 issue of Nature. Full reference
http://www.eurekalert.org/pub_releases/2001-05/NYU-Infr-1605101.htm

Temporal lobe

Maturation of the human brain mapped

The progressive maturation of the human brain in childhood and adolescence has now been mapped. The initial overproduction of synapses in the gray matter that occurs after birth, is followed, for the most part just before puberty, with their systematic pruning. The mapping has confirmed that this maturation process occurs in different regions at different times, and has found that the normal gray matter loss begins first in the motor and sensory parts of the brain, and then slowly spreads downwards and forwards, to areas involved in spatial orientation, speech and language development, and attention (upper and lower parietal lobes), then to the areas involved in executive functioning, attention or motor coordination (frontal lobes), and finally to the areas that integrate these functions (temporal lobe). "The surprising thing is that the sequence in which the cortex matures appears to agree with regionally relevant milestones in cognitive development, and also reflects the evolutionary sequence in which brain regions were formed."
http://www.eurekalert.org/pub_releases/2003-11/sfn-smm110803.htm

November 2001

Separate brain regions for living vs nonliving categories

Lobectomy patients were compared to normal control subjects on a variety of category naming and matching tasks. Patients were disproportionately impaired for naming living things relative to nonliving things. The authors argue that damage to the temporal lobe impairs lexical retrieval most strongly for living things and that the anterior temporal cortices are convergence zones particularly necessary for retrieving the names of living things.
The report appeared in the November issue of Brain and Language. Full reference