Hippocampus Flashcards
Is the hippocampus part of the telencephalon? Does is receive olfactory input?
- the hippocampus is part of the telencephalon
- it receives olfactory input, but lesions to the hippocampus do not disrupt olfactory discrimination
Describe how the hippocampus’s role in memory formation was discovered?
-established in 1957 when Scoville and Milner described cases where anterograde amnesia followed bilateral temporal lobectomies in humans
Kluver-Bucy syndrome
- results from bilateral lesions of medial temporal lobe
- The list of symptoms differs somewhat by source. Generally included are the following:
Amnesia. Characterised by an inability to recall memories. Its nature is both anterograde and retrograde, meaning new memories cannot be formed and old memories cannot be recalled. The level of amnesia is considered to be profound.
Docility. Characterized by exhibiting diminished fear responses or reacting with unusually low aggression. This has also been termed “placidity” or “tameness”.[2][3][4]
Dietary changes and/or Hyperphagia. Characterized by eating inappropriate objects (pica) and/or overeating.[2][3][4]
Hyperorality. This was described by Ozawa et al. as “an oral tendency, or compulsion to examine objects by mouth”.[2][3][4]
Hypersexuality. Characterized by a heightened sex drive or a tendency to seek sexual stimulation from unusual or inappropriate objects.[2][3][4]
Visual agnosia. Characterized by an inability to recognize familiar objects or people.
Patient HM could/did
- remember childhood events
- remember events up to 1-2 years before the surgery
- perform normally on IQ tests
- have normal exteroceptive perception
- learn new motor skills
HM could NOT
- remember having surgery
- recognize his doctors
- understand how he became old
- remember his parents’ death after surgery
- have normal interoceptive perception
- have normal emotional experience
HM showed that the hippocampus probably does NOT:
- store long term memories
- required for memory recall
- required for procedural memory
HM showed that the hippocampus probably IS required for:
- forming new explicit memories
- probably important for memory consolidation
short term memory
-newly acquired information that decays over a brief period of time unless it is reinforced
long term memory
-is retention of acquired information for extended periods of time
The hippocampus proper contains
- CA1
- CA2
- CA3
- CA4
The hippocampal formation contains
- hippocampus proper
- dentate gyrus and subiculum
The hippocampal region contains
- hippocampal formation
- entorhinal cortex
hippocampal sulcus separates the
-dentate from the subiculum
the hippocampus is separated from the rest of the temporal lobe by the
-inferior horn of the lateral ventricle
alveus
-white matter tract containing afferent axons and efferent projections that will enter the fimbria en route to the fornix
where does the fornix carry the ascending projections of the hippocampus to?
- mammillary bodies
- septum
- nucleus accumbens
Name the 3 cell types of the hippocampus and their location
- Pyramidal cells in the CA region
- one large apical dendrite and several smaller basilar dendrites all covered with spines - Granule cells in the dentate gyrus
- round soma and also spiny - inhibitory local circuit neurons located throughout the dentate gyrus and CA regions
The hippocampus circuitry has been called simple and describes as ____. Is that true?
- trisynaptic circuitry
- no, its a misnomer since there are 4 major synaptic connections and several minor ones
Perirhinal inputs to the entorhinal cortex make the __ pathway
-what pathway
parahippocampal cortices project to the entorhinal cortex to make the ___ pathway
-where pathway
The dentate gyrus projects to
-CA3 and these axons are called mossy fibers
the CA3 is the main source of ___ projections to the hippocampus in the ____ hemisphere
- commissural projections
- opposite
Pyramidal cells in the CA3 project to the
-pyramidal cells in the CA1 via Schaffer collaterals
Pyramidal cells in the CA1 project to the
pyramidal cells in the subiculum
the direct input from the ____ cortex (perforant path) synapses on _____ tips of the apical dendrites of CA3 and CA1 cells
- entorhinal cortex
- distal
the indirect input from the ___ (mossy fibers) terminates on ___ dendrites of CA3 neurons
- dentate gyrus
- proximal
Schaffer collaterals from the CA3 synapse onto ___ dendrites of CA_ cells
- intermediate
- CA1
Commissural axons from the contralateral hippocampus form synapses that are relatively ____ on CA3 neurons
-proximal
The strongest inhibitory cells of the hippocampus circuit are ____
-basket cells
In the hippocampus, the overall ratio of excitatory to inhibitory neurons is
20:1
Due to its ratio of excitstory to inhibitory cells, the hippocampus is susceptible to:
- epileptic discharge
- seizure disorders
- ischemic damage
What happens to hippocampul neurons during periods of lack of O2
- ischemic damage can occur from lack of O2 resulting in insufficient ATP production
- this can lead to run-down of the pumps necessary tp remove glutamate from the synapse. Excessive glutamate may stimulate EXCESSIVE Ca2+ influx which causes free radical formation and excitotoxic death
Patient __ had open heart surgery and experienced an episode of brain hypoxia. After recovery it was found he had anterograde amnesia due to profound cell loss restricted to __ bilaterally
- RB
- CA1
Long term Potentiation
- a persistent enhancement of synaptic efficacy
- is a mechanism for how synaptic strength can change with experience
Describe the LTP experiment
- recordings were taken of the dentate granule cells while stimulating the perforant pathway
- first: single pulse stimulations led to stable depolarization of granule cells
- the perforant path was then stimulated at high amplitude and high frequency and this caused a significant increase in the depolarization evoked by single pulses
describe some of the presynaptic alterations observed by LTP
- increased release probability
- increased number of release sites
- increased number of vesicles
describe some of the postsynapic alterations in LTP
- increase in receptor sensitivity
- increase in the number of functional receptors
- alterations in spine structure
