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Memory
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This case consists of the types of memory and their related brain areas. Also there is information about the different types of amnesia and dementia.
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Task 5:Memory
1. What is explicit, implicit, emotional memory, short term/working memory?
A. Long-term explicit memory
Explicit memory for events and facts is conscious and intentional and consists of personal experiences,
or episodic memories and fact-based semantic memories. Both types of explicit memory depend on
conceptually driven top-down processing, in which a person reorganizes the data to store. Later recall of
information is thus greatly influenced by the way in which the information was originally processed.
Episodic memory
Episodic (autobiographic) memory, a person’s recall of singular events is uniquely different from other
neurocognitive memory systems in that it is memory of life experiences centered on the person himself
or herself.
Autonoetic awareness of time
One function of autobiographical memory is providing us with a sense of continuity. Autonoetic
awareness, or self-knowledge, allows us to bind together the awareness of our self as a continuous
entity through time. It further allows us to travel in subjective time, either into the past or into the
future. Patients with hippocampal and frontal cortical injury often lose self-knowledge and have real
difficulty in daily living resulting from a deficit of behavioral self-regulation and the ability to profit from
past experience in making future decisions.
Figure: brain regions of episodic memory. The
uncinate fasciculus is a fiber pathway that
connects the temporal lobe and ventral prefrontal
cortex. Autobiographical memory depends on the
medial temporal lobe and the ventral prefrontal
cortex and the connection between them.
Semantic memory
Knowledge about the world (non-autobiographical) is categorized as semantic memory. It includes the
ability to recognize family, friends and acquaintances; information learned in school such as specialized
vocabularies and reading, writing, and mathematics; and knowledge of historical events.
Not only is semantic memory different from episodic memory, it does not depend on the medial-
temporal-lobe-ventral-prefrontal-lobe memory system that sub-serves episodic memory. Rather,
semantic memory depends on the temporal- and frontal-lobe regions adjacent to the neural regions
that sub-serve episodic memory.
Neural substrates of explicit memory
Neural systems, each consisting of several structures, support different kinds of memory. Figure A
illustrates the neural structures assigned to explicit memory. Most are in the temporal lobe or closely
related to it, including the hippocampus, the rhinal cortices adjacent to the hippocampus in the
temporal lobe, and the prefrontal cortex. Nuclei in the thalamus also participate in as many connections
between the prefrontal cortex and the temporal cortex. The regions that make up the explicit-memory
circuit receive input from the neocortex and from the ascending systems in the brainstem, including the
acetylcholine, serotonin, and noradrenaline activating systems (figure B).
,Hippocampal anatomy
The hippocampus, a limbic structure that extends in a curve from the lateral neocortex of the medial
temporal lobe toward the brain’s midline, has a tube-like appearance. It consists of two gyri, Ammon’s
horn and the dentate gyrus.
Each gyrus contains a distinctive type of cell. Ammon’s horn contains pyramidal cells, and the dentate
gyrus cells are stellate granule cells. The pyramidal cells of Ammon’s horn are divided into 4 groups:
CA1, CA2, CA3 and CA4. These groups are very important for memory and learning.
The hippocampus is reciprocally connected to the rest of the brain through two major pathways:
1. The preforant pathways connects the hippocampus to the posterior temporal cortex.
2. The fimbria fornix connects the hippocampus to the thalamus, prefrontal cortex, basal ganglia
and hypothalamus.
It is through these two pathways that the hippocampus functions as a way station between the
posterior neocortex and the frontal cortex, basal ganglia and brainstem. Within the hippocampus, input
from the neocortex goes to the dentate gyrus, which projects the Ammon’s horn. Thus, granule cells are
the sensory neurons of the hippocampus, and pyramidal neurons are its motor cells.
Hippocampal function
When the hippocampus is damaged:
1. Anterograde memory is more severely affected than retrograde memory
2. Episodic memories are more severely affected than semantic memories
3. Autobiographic memory is especially severely affected
4. Time travel is diminished
The hippocampus may also contribute to our ability to vary memory details when remembering. When
reviewing the difference between the anterior hippocampus and the posterior hippocampus, they
suggest that the anterior hippocampus provides a coarse-grained representation of events, whereas the
posterior area provides a fine-grained representation. By accessing different memory sub-pathways
through the hippocampus we can access and recount either abbreviated or elaborated versions of our
life experiences.
The temporal cortex
One study found that resection has removed portion of temporal cortex adjacent to the hippocampus.
Temporal-lobe areas bordering the rhinal fissure include the perirhinal cortex and the entorhinal cortex,
which provides a major route for neocortical input to the hippocampal formation. These regions, which
project to the hippocampus, are often damaged in patients with medial-temporal-lobe lesions.
Murray used neurotoxic lesions to damage cells and spare fibers to either hippocampus or rhinal cortex
in monkeys, they examine the specific contributions of each structure to amnesia. In the study, monkeys
, reach through the bars of their cages to displace objects under which a reward may be located. To find
the reward, the monkey must use their abilities to recognize objects or recognize a given object in a
given context.
A matching-to-sample task tests object recognition. A monkey sees a sample object that is
displaced to retrieve a food reward hidden underneath. After an interval, the monkey may
choose between the sample and a different object and is rewarded for choosing the familiar
object.
In an alternative non-matching-to-sample version, the monkey must choose the novel object.
Delays can be introduced between the sample and the matching-nonmatching parts of both
tests.
A contextual version of the task requires a monkey to choose an object by using cues based on
the object’s spatial location. The task may require choosing an object that remains in the same
place, or an object that appears in the same location in a visually presented scene in a picture.
Object recognition (factual, semantic) depends on the rhinal cortices, whereas contextual knowledge
(autobiographic, episodic), depends on the hippocampus.
Investigations have revealed that asymmetries in explicit memory exist in all neocortical lobes.
There are significant differences in the memory impairments stemming from damage to the left and
right hemispheres. The temporal neocortex contributes significantly to these functional impairments.
After right-temporal lobe removal, patients are impaired on face-recognition, spatial-position and maze-
learning tests.
Impairments in memory for spatial position are illustrated by performance on the Corsi block-tapping
test, in which a subject learns to tap out a sequence of a block board. Controls learn the repeated
sequence in several trials, although they still have trouble with novel sequences. Subjects with damage
to right temporal lobe either do not learn or learn it very slowly.
Parietal and occipital cortex
Cortical injuries in parietal, posterior temporal and occipital cortices sometimes produce specific long-
term memory difficulties. Many of these deficits appear to develop after bilateral lesions only.
Frontal cortex
The frontal cortex also participates in memory, including autobiographical memory. Usually referred to
as HERA, for hemispheric encoding and retrieval asymmetry, the pattern predicts:
1) Left prefrontal cortex differentially more engaged in encoding semantic information than in
retrieving it
2) Left prefrontal cortex differently more engaged in encoding episodic information than retrieving
it
3) Right prefrontal cortex differentially more engaged in episodic memory retrieval than is the left
prefrontal cortex.
Researchers showed that the left orbitofrontal cortex is preferentially active during memory encoding of
words or series of words, but these regions do not retrieve this information. Rather, the right
dorsolateral prefrontal cortex and the posterior parietal cortex in both hemispheres are active during
memory retrieval.
B. Long-term implicit memory
Implicit memory of learned skills, conditioned reactions and short-term events is non-conscious and
unintentional. Processing is data driven, or bottom-up, and depends simply on sensory or motor
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