Question

Traumatic events can sometimes become over-expressed memories; when these highly detailed memories are recalled, they are vividly re-lived, as if the emotional trauma is being experienced for the first time.

A. What does this suggest about the influence the amygdala has over the hippocampus?

B. For both structures, in your own words, write 2-3 sentences* describing:

1. their location in the brain
2. their neurological relationship to each other and nearby structures
3. any neurologic disorders associated with their dysfunction.

Answer 1

Typically the term "memory" refers to the ability to consciously remember past experiences or previously learned information. This kind of memory is considered to be dependent upon the hippocampal system. However, our emotional state seems to considerably affect the way in which we retain information and the accuracy with which the retention occurs. The amygdala is the most notably involved brain structure in emotional responses and the formation of emotional memories

hippocampal outcome of amygdala activation may be critically dependent on four main factors: (1) The intensity of amygdala activation, (2) the temporal relation between the activation of the amygdala and the hippocampus dependent memory function, (3) the duration of amygdala activation, and (4) the contextual input during the processing of the information.

Amygdala and hippocampus can operate independently and interact in subtle ways. Understanding the intricacies of their anatomical structure and their projection circuitry is of great importance given that amygdala and hippocampus are implicated in a wide range of emotional diseases and emotion-associated memory impairment, including anxiety, depression and Alzheimer’s disease (AD),

Anatomy and Physiology of Basolateral Amygdala Subregions

Amygdala nuclei are divided into three groups: (1) basolateral amygdala groups (BLA), which contains the lateral nucleus (L or LA), the basal nucleus (BA) and basomedial (BM) nucleus; (2) cortical-like groups, which comprises nucleus of the lateral olfactory tract and the cortical nuclei; and (3) the centromedial groups, which includes the medial and central nuclei. In the coronal sections from rostral to caudal of the brain, the basal nucleus (also termed basolateral nucleus) can be further divided into arterial part (BLA) and posterior part (BLP). Therefore, BLA has been used to represent basolateral amygdala and the anterior part of basolateral nucleus of amygdala , respectively

Lateral Nucleus

Anatomically, the lateral nucleus (LA) is located in the dorsolateral part of the amygdala. It intensively receives extrinsic sensory inputs, meanwhile, sends projections to other amygdala nuclei. So, LA is functionally viewed as an input region of amygdala and origin of many intra-amygdaloidal projections. On the basis of cytoarchitectonics, LA can be further divided into three subdivisions: dorsolateral (the smaller), ventrolateral (the larger) and the medial subdivisions.LA also sends projections to basolateral nucleus, periamygdaloid cortex, the dorsal portion of the central division of the medial nucleus, the posterior cortical nucleus, the capsular division of the central nucleus, and the lateral division of the amygdalo-hippocampal area, but in relatively less magnitude

unique molecular and cellular mechanisms in LA may contribute to different stages of fear memory formation

Basolateral Nucleus

Basolateral nucleus (BL) is also called basal nucleus. It locates ventrally to the LA and includes three subdivisions, i.e., rostral magnocellular subdivision, caudal intermediate and parvicellular subdivisions. The last two are densely innervated by LA.BL plays an integral role in anxiety. Patients suffering from anxiety show abnormal activity of BL

It is also well-established that BL plays a crucial role in reward behavior

Basomedial Nucleus

Basomedial nucleus (BM) lies ventrally to the BL and is subdivided into the parvicellular subdivision, the magnocellular subdivision and the intermediate subdivision.

BM bridges the connection between LA and the central nucleus (CeM), which is the output region contributing most amygdala projections to the brainstem fear effectors. Also, BM projects to several anxiolytics brain regions, such as anterodorsal nucleus of the bed nucleus of the striaterminalis (BNST) and the ventral medial prefrontal cortex

Photoactivation of BM suppresses high-anxiety states and fear-related freezing while optogenetic or pharmacological inhibition of the BM increases anxiety and freezing.

Anatomy and Physiology of Hippocampus Formation

Hippocampus is a critical structure involved in spatial and nonspatial memory . Along its longitudinal axis, hippocampus can be functionally divided into dorsal, intermediate and ventral parts ,and it can be further divided into CA1, CA3 and dentate gyrus (DG) along the transverse axis. There is a canonical trisynaptic loop within hippocampus: from the input node of DG to CA3 and finally to the output node CA1

The ventral hippocampus is responsible for affective and motivated behaviors through its distinct target areas.

at BLA and hippocampus can also act synergistically. In anxiety-related behaviors, neurons in BLA and hippocampus fire actively, indicating their neural correlation. In contextual fear conditioning, inactivation of the BLA with muscimol, a GABAA receptor agonist, attenuates the consolidation of hippocampus-dependent context memory .. In addition, BLA manipulation alters genes expression and synaptic plasticity of the hippocampus . Although these studies indicate that BLA could modulate hippocampus-dependent behavior via their neural correlation, it should be noted that these effects are not necessarily indicative of a direct, monosynaptic BLA-hippocampus projection, because these pharmaceutical injection of BLA and in vivo electrophysiology recording may inevitably manipulate multiple circuits between BLA and hippocampus. The mPFC is one of such regions forming synapses with both BLA and hippocampus. It bidirectionally connects with amygdala and receives projections from hippocampus simultaneously Thus, dissection of monosynaptic BLA-hippocampus projection is urgently needed to elucidate how BLA and hippocampus interact directly to account for emotion-regulated memories.

2

The amygdala is an almond-shaped structure in the brain; its name comes from the Greek word for “almond”. As with most other brain structures, you actually have two amygdalae (shown in red in the drawing here). Each amygdala is located close to the hippocampus, in the frontal portion of the temporal lobe.

The hippocampus is located under the cerebral cortex in the allocortex, and in primates it is in the medial temporal lobe. It contains two main interlocking parts: the hippocampus proper (also called Ammon's horn) and the dentate gyrus.

damage of the amygdala in genetic disorders such as lipoid proteinosis (Urbach-Wiethe disease) support its role in many aspects of emotional processing, including recognition of emotional expression in faces. The amygdala is affected in several neurologic disorders and psychiatric disorders including Alzheimer disease (AD), temporal lobe epilepsy (TLE), and anxiety, and depression

The hippocampus, and in particular the CA1 region, is vulnerable to metabolic stress. This affection can be observed in acute neurological disorders such as ischaemia, limbic encephalitis, hypoglycaemic encephalopathy, epilepsy, multiple sclerosis, and transient global amnesia.

PTSD

Some studies shows correlation of reduced hippocampus volume and posttraumatic stress disorder (PTSD).

Transient global amnesia

Transient global amnesia is a dramatic, sudden, temporary, near-total loss of short-term memory

Schizophrenia

The causes of schizophrenia are not well understood, but numerous abnormalities of brain structure have been reported. The most thoroughly investigated alterations involve the cerebral cortex, but effects on the hippocampus