Temporal Lobe
The temporal lobe is a collection of diverse abilities. The
most obvious specialization is sound reception and memory. Sound is turned into
language or music in the temporal lobe. Deep inside the lobe is the amygdala,
the center of emotions, vital to survival. The medial temporal lobe is a critical processor of the acquisition and
recall of new memories. Without normal medial temporal lobe function, working
memory cannot be translated into longer-term storage. There are at least two
aspects of episodic memory: 1. Content or recall of an event and 2. Source-associated information about when and how the episode occurred.
The medial temporal region is critical for both source and content memory.
Kolb and Wishaw
identified eight symptoms of temporal lobe damage: 1) disturbance of auditory
sensation and perception, 2) disturbance of selective attention of auditory and
visual input, 3) disorders of visual perception, 4) impaired organization and
categorization of verbal material, 5) disturbance of language comprehension, 6)
impaired long-term memory, 7) altered personality and affective behavior, 8)
altered sexual behavior.
Temporal lobe seizures produce a variety of extraordinary
experiences. Ko and Sahai-Srivastava
described some common features:" Auras occur in approximately 80% of temporal
lobe seizures. They are a common feature of simple partial seizures and usually
precede complex partial seizures of temporal lobe origin. Auras may be
classified by symptom type; the types comprise somatosensory, special sensory,
autonomic, or psychic symptoms. Somatosensory and special sensory phenomena. Olfactory and gustatory illusions and hallucinations may occur. Acharya et al
found that olfactory auras are more commonly associated with temporal lobe
tumors than with other causes of temporal lobe epilepsy. Auditory hallucinations consist of a buzzing sound, a voice or voices, or
muffling of ambient sounds. This type of aura is more common with neocortical
temporal lobe epilepsy than with other types of temporal lobe epilepsy. They
stated: "Patients may report distortions of shape, size, and distance of objects.
These visual illusions are unlike the visual hallucinations associated with
occipital lobe seizure in that no formed elementary visual image is noted, such
as the visual image of a face that may be seen with seizures arising from the
fusiform or the inferior temporal gyrus. Things may appear shrunken (micropsia) or larger (macropsia) than usual.
Tilting of structures has been reported. Vertigo has been described with
seizures in the posterior superior temporal gyrus. Patients may have a feeling of
déjà vu or jamais vu, a sense of familiarity or unfamiliarity, respectively.
Patients may experience depersonalization (ie, feeling of detachment from
oneself) or derealization (i.e. surroundings appear unreal).Fear or anxiety usually is associated with seizures arising from the
amygdala. Sometimes, the fear is strong, described as an "impending sense of
doom." Patients may describe a sense
of dissociation or autoscopy, in which they report seeing their own body from
outside."
Medial Temporal Lobe
The identification of the medial temporal lobe, especially the hippocampus as
a critical processor of memory began with studies of amnesia in humans following
removal of the hippocampus. Without normal medial temporal lobe function,
working memory cannot be translated into longer-term storage. There are at least two aspects of episodic memory: 1. Content or recall of an
event and 2. Source-associated information about when and how the episode
occurred. The medial temporal region is critical for both source and content
memory.
We know, for example, that the CA1 layer of the hippocampal cortex is a
processor of incoming information, but we do not appreciate exactly how this
works. John Lisman suggested: "In addition to its role as a decoder, CA1 may
also have a role in making a match/mismatch computation in which sensory
''reality'' arriving directly from the entorhinal cortex is compared with
predictions of reality made by dentate–CA3. This idea relates to the proposal
that the brain forms a model of the world based on past events. This model
requires stored sequences that allow prediction of expected events. The brain
continuously compares these expectations with events. If the comparison shows a
''mismatch'' to expectations or something altogether novel, memory encoding and
attention processes are triggered. Evidence that the human hippocampus is
involved in such processes comes from brain imaging. Related experiments show
that hippocampal neurons become habituated to a repetitive stimulus but respond
vigorously when the standard stimulus is replaced by an ''oddball'' stimulus.
Other experiments in rat directly show activity related to match/mismatch
conditions. The clearest demonstration of the existence of an internal model
comes from experiments in which a repetitive stimulus was suddenly omitted.
Cells in the mammillary body, one of the recipients of hippocampal output, fire
in exact registration with the expected onset and duration of the absent
stimulus.Because the CA1 region is the site of convergence of predictions
from CA3 (via the Schaffer collaterals) and raw sensory information (via the
perforant path input from the cortex), CA1 is well positioned to perform a
match/mismatch computation."
One of the properties of the hippocampus is a cognitive-spatial map, a series
of neuronal networks in which environmental features are encoded in terms of an
animal's location and 
navigational cues. Aggleton and Brown
suggested that the parahippocampal, perirhinal, entorhinal cortices
and the hippocampus form a medial temporal memory system that acquires and holds
new information, some of which may eventually be stored in the neocortex as
longterm memory. They viewed the hippocampus as a mixer which combines different
components of the memory. The area around the hippocampus can store
representations of individual items while the hippocampus itself organizes
memories according to relationships among items, including spatial
relationships.
Eichenbaum et al proposed: “ that individual hippocampal cells encode
regularities present in the animal's every experience, including spatial and
nonspatial cues and behavioral actions… the coding of spatial locations by
hippocampal place cells emerges from a fundamental representation of behavioral
episodes. These representations involve a network of cells, each of which
represents a temporally defined event…the hippocampus is central to
episodic memory…episodic representations are tied to one another within a
general memory organization, consistent with the common notion that networks of
semantic knowledge are built from episodic experiences.”
Burgess et al suggested:” Finding one's way around an environment
and remembering the events that occur within it are crucial cognitive abilities
that have been linked to the hippocampus and medial temporal lobes. Our review
concentrates on important concepts in this field: spatial frameworks,
dimensionality, orientation and self-motion… While processing of spatial scenes
involves the parahippocampus, the right hippocampus appears particularly
involved in memory for locations within an environment, with the left
hippocampus more involved in context-dependent episodic or autobiographical
memory.”
