Limbic system

Chronic stress changes the architecture of the hippocampus, leading to depression and cognitive impairment

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

This 2014 rodent study gave further details that:

“Chronic stress, which can precipitate depression, induces changes in the architecture and plasticity of apical dendrites that are particularly evident in the CA3 region of the hippocampus.”

Other studies on the hippocampus CA3 region include:

http://www.pnas.org/content/111/45/16130.full “Role for NUP62 depletion and PYK2 redistribution in dendritic retraction resulting from chronic stress”

Problematic research: Is sleep deprivation a therapy for depression? Seriously?

gettingwell4 0-1 star Wasted resources, Limbic system

This 2013 Zurich study provided details of depression symptoms, particularly in limbic system structures.

As often happens when researchers are absorbed in studying symptoms, there was nothing about treating the causes, in this case, of depression.

Sleep deprivation as a viable therapy for enduring depression? Is that or drugs really all that science has to offer for depression?

http://www.pnas.org/content/110/48/19597.full “Sleep deprivation increases dorsal nexus connectivity to the dorsolateral prefrontal cortex in humans”

The thalamus’ role in coordinating REM sleep stages

gettingwell4 2-3 stars Required further work, Brainstem, Limbic system, Lower brain, Memory, Thalamus

This 2013 human study provided more details about dream sleep. The thalamus portion of the limbic system coordinates REM stages, which play critical roles in learning and memory.

This study also noted that science assigns no functions to dreams themselves, which was the first I’d heard of it.

http://www.pnas.org/content/110/25/10300.full “Rhythmic alternating patterns of brain activity distinguish rapid eye movement sleep from other states of consciousness”

Problematic research: Feigning naivety of the impact of prenatal, infancy and early childhood experiences

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

What I found curious in this 2012 UK review of 82 studies was the reviewer’s reluctance to highly regard a human’s life before birth, during infancy, and in early childhood.

There was no lack in 2012 of animal studies to draw from to inferentially hypothesize how a human fetal environment causes the fetus to adapt with enduring epigenetic changes.

To take just one study that I won’t curate on this blog because it’s too old:

Weinstock M (2008) The long-term behavioural consequences of prenatal stress. Neurosci Biobehav Rev 32:1073–1086, “Stress, [to the pregnant mother] in rodents as well as nonhuman primates, produces behavioral abnormalities [in the pup], such as

  • an elevated and prolonged stress response,
  • impaired learning and memory,
  • deficits in attention,
  • altered exploratory behavior,
  • altered social and play behavior, and
  • an increased preference for alcohol.”

Yet the reviewer posed the question:

“There is a need to determine just what epigenetic changes do and do not account for. Put succinctly, do they explain individual differences in response to adversity and do they account for variations in health and behavior outcomes?”

I suspect that the cause of this feigned naivety was the political incorrectness of adequately placing importance in the human fetus’ experience of the development environment provided by their mother.

The PC view would have us pretend that there aren’t lasting adverse effects from human prenatal, infancy, and early childhood experiences.

The follow-on pretense to this PC view would be that later-life consequences aren’t effects, but are instead, mysteries due to “individual differences.”

http://www.pnas.org/content/109/Supplement_2/17149.full “Achievements and challenges in the biology of environmental effects”

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Stress impairs the normal matching of neuronal activity to increased blood flow in the amygdala

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Cortisol, Limbic system, Neurochemicals, Stress

This 2014 rodent study showed one aspect of how stress changed the amygdala. Stress didn’t allow normal matching of neuronal activity to increased blood flow:

“Chronic stress — which is a contributing factor for many diseases — impairs neurovascular coupling in the amygdala..

Neurovascular coupling (is) the process that matches neuronal activity with increased local blood flow.”

http://www.pnas.org/content/111/20/7462.full “Stress-induced glucocorticoid signaling remodels neurovascular coupling through impairment of cerebrovascular inwardly rectifying K+ channel function”

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”

Active areas of the brain when making decisions in stressful conditions

gettingwell4 2-3 stars Required further work, Cerebrum, Cortisol, Limbic system, Lower brain, Memory, Neurochemicals, Stress

This 2013 human study was of decision making under stressful conditions.

Acute stress (ice water immersion) evoked habitual behavior rather than deliberative behavior. In my view, the subjects’ behaviors when under stress were driven more by their limbic system and lower brain areas than their cerebrum.

This finding wasn’t a big surprise. However, the researchers went on to state:

“Subjects with more executive resources to spare find themselves less susceptible to the behavioral changes brought about by stress response.”

I interpreted this statement to mean that when stressed, the more-capable subjects didn’t act out as much as the less-capable subjects acted out their respective feelings, instincts and impulses.

I felt that to understand this statement called for more investigation into the individual histories of the subjects:

  • What happened in their lives that enabled each person to acquire “more executive resources” or not?
  • What happened in their lives that made each person more or less sensitive to stress?
  • How are these two avenues of investigation related?

http://www.pnas.org/content/110/52/20941.full “Working-memory capacity protects model-based learning from stress”

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”

The effects of early-life stress are permanent alterations in the child’s brain circuitry and function

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Brain development, Cortisol, Limbic system, Memory, Neurochemicals, Stress ,

The sobering application of this 2013 rodent study’s finding was that if the limbic systems of human children weren’t already permanently damaged before they entered an orphanage, the orphanage experience would probably do that to them:

“The current study manipulates the type and timing of a stressor and the specific task and age of testing to parallel early-life stress in humans reared in orphanages.

The results provide evidence of both early and persistent alterations in amygdala circuitry and function following early-life stress.

These effects are not reversed when the stressor is removed nor diminished with the development of prefrontal regulation regions.”

http://www.pnas.org/content/110/45/18274.full “Early-life stress has persistent effects on amygdala function and development in mice and humans”

One way that mothers cause fear and emotional trauma in their infants

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

This 2014 rodent study showed that infants learned to fear specific items in the environment that their mothers feared. The imprinting memory happened at a stage in the infants’ lives when they hadn’t yet developed the physiology to respond to the environment with fear on their own.

The learning cue was the mothers’ fear response – in this case, her distress odor, even when the mother was not present – coupled with the infants’ stress. The fear memory was stored in the infants’ amygdalae:

“These memories are acquired at younger ages compared with amygdala-dependent odor-shock conditioning and are more enduring following minimal conditioning.

Our results provide clues to understanding transmission of specific fears across generations and its dependence upon maternal induction of pups’ stress response paired with the cue to induce amygdala-dependent learning plasticity.”

There’s no scientific reason why this and related studies shouldn’t inform researchers who ignore the earliest stages of human life when studying limbic system disorders in humans.

For an example of researchers choosing to NOT be informed, look at Is this science, or a PC agenda? Problematic research on childhood maltreatment and its effects.

http://www.pnas.org/content/111/33/12222.full “Intergenerational transmission of emotional trauma through amygdala-dependent mother-to-infant transfer of specific fear”

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”