Hippocampus

Thalamus gating and control of the limbic system and cerebrum is a form of memory

gettingwell4 5+ stars Premium, Cerebrum, Hippocampus, Hypothalamus, Limbic system, Memory, Thalamus ,

This 2014 German rodent study showed how the thalamus actively controlled and gated information to and from the cerebrum.

The researchers elaborated in news coverage on how thalamic control and gating represented a form of memory:

“Q. When asked if, given that

  1. Sensory signals en route to the cortex undergo profound signal transformations in the thalamus,
  2. A key thalamic transformation is sensory adaptation in which neural output adjusts to statistics and dynamics of past stimuli, and
  3. The thalamus, hypothalamus and hippocampus being part of the limbic system, might memory reconsolidation play a role in the cortico-thalamic pathway?

A. “It’s conceivable that the cortico-thalamic pathway is subject to long term plasticity,” Groh conjectures. “In fact, on a synaptic level, these inputs can change their strength and retain adjusted strengths for long periods. This process represents another – albeit much slower – form of adaptation which some interpret as memory.”

Q. Conversely, might the thalamic-cortical pathway affect memory?

A. “If particular sensory-evoked activity patterns would cause long-term changes in the cortico-thalamic pathway, and thereby change the way incoming signals are processed before reaching the cortex,” he opines, “then this would indeed reflect a form of information storage.”

In other words, there are ways in addition to our usual ideas about memory that the limbic system remembers.

Other items in news coverage included:

“Rodents, cats, primates and humans show a common architecture of two feedback pathways from cortex to thalamus in the auditory, visual and somatosensory (but not olfactory) systems.

In this study we looked at processing of touch information, and we’d like to know how homologous pathways affect visual or auditory processing. It’s fascinating that despite fundamental differences between visual, auditory and somatosensory signals, basic layouts of thalamocortical systems for each modality are quite similar.”

Other areas of research that might benefit from their study include any medical research involving the thalamocortical system that might involve inappropriate gating of sensory signals.

For a given stimulus, output neural response will not be static, but will depend on recent stimulus and response history.”

http://www.pnas.org/content/111/18/6798.full “Cortical control of adaptation and sensory relay mode in the thalamus”

A mother’s care affects the infant’s hippocampus structure and function through epigenetic regulation of genes

gettingwell4 4-5 stars Advanced knowledge, Brain development, Epigenetics, Glutamate, Hippocampus, Limbic system, Memory, Neurochemicals, Stress

This 2012 McGill University rodent study found:

“Variations in maternal care in the rat affect hippocampal morphology and function as well as performance on hippocampal-dependent tests of learning and memory in the offspring.

Thus, in the rat, as in humans, social influences operate during early life to influence the structure and function of brain regions critical for cognitive capacity.

Variations in maternal care can influence hippocampal function and cognitive performance through the epigenetic regulation of genes.”

http://www.pnas.org/content/109/Supplement_2/17200.full “Variations in postnatal maternal care and the epigenetic regulation of metabotropic glutamate receptor 1 expression and hippocampal function in the rat”

Is this science, or a PC agenda? Problematic research on childhood maltreatment and its effects

gettingwell4 < 0 Detracted from science, Amygdala, Brain development, Epigenetics, Hippocampus, Limbic system, Lower brain, Memory, Stress ,

This 2013 Wisconsin human study’s goal was to assess effects of childhood trauma using both functional MRI scans and self-reported answers to a questionnaire. The families of the study’s subjects (64 18-year-olds) participated with researchers before some of the teenagers were born.

How could the teenagers give answers that described events that may have taken place early in their lives, before their cerebrums were developed, around age 4? Even if the subjects were old enough to remember, would they give accurate answers to statements such as:

“My parents were too drunk or high to take care of the family.

Somebody in my family hit me so hard that it left me with bruises or marks.”

knowing that affirmative answers would prompt a visit to their family from a government employee?

Although some data may have been available, data from the teenagers’ prenatal, birth term, infancy, and early childhood wasn’t part of the study design. Intentional dismissal of early influencing factors ignored applicable research!

No

Was the study’s limited window due to the political incorrectness of placing importance in the development environment provided by the subjects’ mothers? The evidence was there for those willing to see.

One clue of ignored early traumatic events was provided by the lead researcher’s quote in news coverage:

“These kids seem to be afraid everywhere,” he says. “It’s like they’ve lost the ability to put a contextual limit on when they’re going to be afraid and when they’re not.”

This finding of “fear without context” possibly described the later-life effects of traumas that were encountered in utero and during infancy. A pregnant woman’s terror and fear can register on the fetus’ lower brain and the amygdala from the third trimester onward.

Storing a memory’s context is one of the functions that the hippocampus performs. Because the hippocampus develops later than the amygdala, though, it would be unable to provide a context for any earlier feelings and sensations such as fear and terror.

The researchers attempted to place the finding of unfocused fear into later stages of child development without doing the necessary research. They tried to force this finding into the subjects’ later development years by citing rat fear-extinction and other marginally related studies.

But citing these studies didn’t make them applicable to the current study. Cause and effect wasn’t demonstrated by noting various “is associated with” findings.

Was this science? Was it part of furthering an agenda like protecting publicly funded jobs?

Was this study published to make a contribution to science? Were the peer reviewers even interested in advancing science?

And what about the 64 18-year-old subjects? If the lead researcher’s statement was accurate, did these teenagers receive help that addressed what they really needed?

http://www.pnas.org/content/110/47/19119.full “Childhood maltreatment is associated with altered fear circuitry and increased internalizing symptoms by late adolescence”

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When recognition memory is independent of hippocampal function

gettingwell4 2-3 stars Required further work, Cerebrum, Hippocampus, Limbic system, Memory

This 2014 human study provided additional details on the specialized brain circuits we have for recognizing faces.

Damage to the hippocampus didn’t impair recognition of new faces, “..but only at a short retention interval. Recognition memory for words, buildings, famous faces, and inverted faces was impaired.”

http://www.pnas.org/content/111/27/9935.full “When recognition memory is independent of hippocampal function”

Conserved epigenetic sensitivity to early life experience in the hippocampus

gettingwell4 2-3 stars Required further work, Brain development, Epigenetics, Hippocampus, Limbic system, Stress ,

This 2012 human study was done by McGill University, whose researchers in Canada are at the forefront of epigenetic studies. The subject was epigenetic DNA methylation in the hippocampus of people who experienced abuse as children and who also committed suicide.

Comparisons were made with rats that were stressed in early life to identify genomic regions that are epigenetically changeable in response to a range of early life experiences.

http://www.pnas.org/content/109/Supplement_2/17266.full “Conserved epigenetic sensitivity to early life experience in the rat and human hippocampus”

Left–right dissociation of hippocampal memory processes in mice

gettingwell4 2-3 stars Required further work, Brain hemispheres, Hippocampus, Limbic system, Memory

This 2014 rodent study provided more details on the CA3 segment of the hippocampus:

“Silencing of either the left or right CA3 was sufficient to impair short-term memory…

Only left CA3 silencing impaired performance on an associative spatial long-term memory task, whereas right CA3 silencing had no effect.”

http://www.pnas.org/content/111/42/15238.full “Left–right dissociation of hippocampal memory processes in mice”

Hippocampal mechanisms involved in the enhancement of fear extinction caused by exposure to novelty

gettingwell4 2-3 stars Required further work, Amygdala, Hippocampus, Limbic system, Memory

This 2014 Brazilian rodent study provided more information on the workings of the hippocampus. The researchers measured the effects of re-experiencing a fear within a specific context:

“Within a restricted time window, a brief exposure to a novel environment enhances the extinction of contextual fear.

The enhancement of extinction by the exposure to novelty depends on hippocampal gene expression..on hippocampal but not amygdalar processes.”

http://www.pnas.org/content/111/12/4572.full “Hippocampal molecular mechanisms involved in the enhancement of fear extinction caused by exposure to novelty”

Problematic research on the hippocampus part of the limbic system

gettingwell4 0-1 star Wasted resources, Hippocampus, Limbic system, Memory

This 2014 UK human study of the CA3 region of the hippocampus found:

“Individual differences in subjective mnemonic experience can be accurately predicted from measurable differences in the anatomy and neural coding of hippocampal region CA3.”

I emailed the authors as follows:

“I read the “CA3 size predicts the precision of memory recall” study, and I wondered how it could be used to help people.

I am not a scientist; I am a software developer by trade. I read the abstracts of each new issue of PNAS with an eye to how studies can help people, which I think is an implied reason to publicly fund research.

The study’s supporting information reveals that the participants scored no emotional involvement with the tasks’ memories. This variable thus did not influence the finding that the contexts of participants’ memories were not a factor.

Could it be that the study’s findings apply to only non-emotional memories, and that context could be a factor in memories that involve emotions?

Given the large role of the hippocampus in our emotional memories, would it not have been realistic to include emotional content in the study? Was it a design decision to not involve the participants’ emotions?

The study found that memory retrieval confusion increased with a participant’s smaller CA3 size. We know from studies such as http://www.pnas.org/content/109/9/E563.full “Childhood maltreatment is associated with reduced volume in the hippocampal subfields CA3, dentate gyrus, and subiculum” and its references that emotional experiences influence CA3 anatomy.

Could it be that the study’s participants were not all sampled from the same brain population?”

http://www.pnas.org/content/111/29/10720.full “CA3 size predicts the precision of memory recall”

Early emotional experiences change our brains: Childhood maltreatment is associated with reduced volume in the hippocampus

gettingwell4 4-5 stars Advanced knowledge, Brain development, Hippocampus, Limbic system, Stress ,

This 2011 human study by the grandfather of hippocampus stress studies, Martin Teicher, quantified childhood maltreatment using the Adverse Childhood Experiences study and Childhood Trauma Questionnaire scores:

“The strongest associations between maltreatment and volume were observed in the left CA2-CA3 and CA4-DG [dentate gyrus] subfields, and were not mediated by histories of major depression or posttraumatic stress disorder.

These findings support the hypothesis that exposure to early stress in humans, as in other animals, affects hippocampal subfield development.”

The evidence is clear that early emotional experiences change our brains. There are seldom valid reasons for researchers to exclude emotional content when designing human brain studies, especially studies that involve the hippocampus.

http://www.pnas.org/content/109/9/E563.full “Childhood maltreatment is associated with reduced volume in the hippocampal subfields CA3, dentate gyrus, and subiculum”

Let’s not miss a big clue! Embryonic precursor transplants in adult hippocampus

gettingwell4 0-1 star Wasted resources, Brain development, Hippocampus, Limbic system ,

This 2014 rodent study induced “multiple psychosis-relevant phenotypes“ by disrupting specific functions of the hippocampus. The researchers then “cured” the brain disorders:

“Transplanting interneuron progenitors derived from the embryonic medial ganglionic eminence into adult hippocampus mitigates these abnormalities.”

However, full function of the hippocampus wasn’t restored.

I disagree that this study’s findings:

“Support a rationale for targeting limbic cortical interneuron function in the prevention and treatment of schizophrenia.”

People with schizophrenia aren’t lab rats and shouldn’t be treated as such. They often don’t need something externally done to them to recover from brain disorders.

Doesn’t the fact that embryonic precursors to the adult brain helped “cure” the abnormalities tell us where to look for the disorders’ beginnings? Let’s not miss a big clue as to when brain disorders may start.

http://www.pnas.org/content/111/20/7450.full “Interneuron precursor transplants in adult hippocampus reverse psychosis-relevant features in a mouse model of hippocampal disinhibition”

Problematic research: Hippocampal memory reactivation during rest supports upcoming learning of related content

gettingwell4 0-1 star Wasted resources, Cerebrum, Hippocampus, Limbic system, Memory

This 2014 human study involved the subjects replaying hippocampal memories in the limbic system while in a restful state.

The researchers found that intentional replaying made memories stronger, and improved understanding of future related material.

However, the researchers excluded emotional memories from this study. See the human Emotional memories and out-of-body–induced hippocampal amnesia study as an example of why emotional memories are necessary in order to properly study the hippocampus. Also see Problematic research on memory for why excluding emotional memories yields questionable findings.

http://www.pnas.org/content/111/44/15845.full “Memory reactivation during rest supports upcoming learning of related content”

Hippocampus replays memories and preplays to extend memories into future scenarios

gettingwell4 4-5 stars Advanced knowledge, Hippocampus, Limbic system, Memory

This 2013 MIT rodent study of the hippocampus portion of the limbic system focused on the “place” cells in the CA1 segment of the hippocampus.

During rest and sleep, the subjects’ hippocampi replayed and consolidated memories. They also preplayed events in the place cells to imagine future scenarios of “novel spatial experiences of similar distinctiveness and complexity.”

Hippocampal preplaying was advantageous when venturing into new locations because:

“The selection of specific sequences from a larger preconfigured repertoire confers the hippocampal network with the capacity to rapidly encode multiple parallel novel experiences.”

http://www.pnas.org/content/110/22/9100.full “Distinct preplay of multiple novel spatial experiences in the rat”

Emotional memories and out-of-body–induced hippocampal amnesia

gettingwell4 5+ stars Premium, Hippocampus, Limbic system, Memory, Stress

I was happy to see that the researchers in this 2014 Swedish human study included emotional memories when studying the hippocampus. They demonstrated that including emotional memories wasn’t that difficult to do.

In fact, this study’s researchers deemed emotional memories to be necessary in order to properly study the hippocampus, as evidenced by this statement about the experiment’s scripts:

“The selected life events had a moderate emotional level to ensure episodic long-term memory encoding.”

It made me wonder whether there are scientific bases for why other researchers go to such lengths to avoid including emotions in human memory studies.

Also:

“The experiments revealed two important findings. First, the behavioral results showed that episodic encoding of life events requires perceiving the world from the first-person perspective centered on one’s real body, and violations of this basic condition produced impaired episodic recall, indicative of fragmented encoding.

Second, the brain imaging data demonstrated that encoding events experienced out-of body specifically impacts the activation of the left posterior hippocampus during retrieval, suggesting an impaired hippocampal binding mechanism during encoding.

These findings are fundamentally important, as they suggest a link between the ongoing perceptual experiences of the body and the world from the first-person perspective and the hippocampal episodic memory system.”

To conclude:

“Given the apparent requirement of a natural first-person perspective between the body and the world for intact hippocampal memory function, a dissociative out-of-body experience during an acutely stressful event could, by itself, impair the encoding mechanism and produce fragmented, spatiotemporally disorganized memories.”

http://www.pnas.org/content/111/12/4421.full “Out-of-body–induced hippocampal amnesia”

Similarity in form and function of the hippocampus in rodents, monkeys, and humans

gettingwell4 2-3 stars Required further work, Brain development, Hippocampus, Limbic system, Stress , ,

This 2013 study had something for the anti-evolutionists to chew on.

Is it anti-evolutionary for human brain and behavior researchers to not be informed by animal studies such as those that show prenatal hippocampal damage done to the fetus by the mother’s environment?

http://www.pnas.org/content/110/Supplement_2/10365.full “Similarity in form and function of the hippocampus in rodents, monkeys, and humans”

Problematic research on memory

gettingwell4 < 0 Detracted from science, Cerebrum, Hippocampus, Limbic system, Memory

This 2013 Harvard human study investigated brain areas that stabilized and updated memories when reactivated:

“The timing of neural recruitment and the way in which memories were reactivated contributed to differences in whether memory reactivation led to distortions or not.

Stronger reliving improved memory.”

However, like researchers often do, they stripped all emotional memory content out of the study, presumably because messy feelings would confound their conclusions. The study used non-emotional pictures only.

The researchers wanted to apply this study to eyewitness accounts. What are the chances that an eyewitness to a murder or a violent accident or crime would have a non-emotional memory of the event?

The study’s exclusion of emotional memories called into doubt that the finding “stronger reliving improved memory” also applied to reliving emotional memories. The categorical statements the researchers claimed about memory, in particular about the hippocampus – the center of emotional memories – weren’t shown to be applicable to emotional memories.

Also, the researchers didn’t include areas of the limbic system, other than the hippocampus, that would likely participate in the reliving of emotional memories. The Making lasting memories: Remembering the significant summary study cited many studies that provided evidence of other brain areas’ involvement.

The researchers had too narrow a basis for a finding that applied across the spectrum of what can be termed memory.

http://www.pnas.org/content/110/49/19671.full “Neural mechanisms of reactivation-induced updating that enhance and distort memory”