Post on 15-Feb-2017
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
The Limbic SystemN.Bèchet-Dept of Neuroscience
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Key Concepts What is the limbic system?
The Papez circuit
The hippocampus & memory formation
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System Not any one structure or neural circuit, rather:
Various brain structures that are related functionally and/or anatomically
Several interconnected nuclei & cortical regions
In a single sentence the function of this system: Control of self and species preservation This encompasses:
Emotion, level of arousal, motivation, reinforcing behaviors & memory
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System-Nomenclature On the medial aspect of each hemisphere the
cortex forms a ring
This ring coincides with the edge (limbus) of the cortex Hence the term “Limbic system” came about
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System-Nomenclature
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System-Components Still debated amongst those in neuroscience, however these structures are generally
accepted as forming part of the system: Insular cortex Olfactory bulb Hippocampus Amygdala Orbital frontal cortex (OFC) Hypothalamus Subcallosal gyrus Septal nuclei Cingulate gyrus Thalamic nuclei Parahippocampul gyrus Mammillary bodies
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System-Classification 2 accepted classification systems:
1)-Location of structure: Cortical structures
Cingulate gyrus Parahippocampul gyrus Subcallosal gyrus Insular cortex OFC Hippocampus
Collectively referred to as the “Limbic lobe”
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System-Classification 2 accepted classification systems:
1)-Location of structure: Sub-cortical structures
Amygdala Hypothalamus Thalamus Olfactory bulb Mammillary bodies Septal nuclei
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Limbic System-Classification 2 accepted classification systems:
2)-Function of structure: Input
Limbic lobe Amygdala
Output Hypothalamus Septal nuclei Amygdala
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Peripheral Feedback Theory In 1890 William James asked an important question:
What is the nature of fear? Do we run away from the bear because we are afraid or are we afraid because we are running away?
According to him it was the latter, he proposed: The conscious experience of fear is a consequence of
emotional responses These bodily changes that occur in the process of running
away
We are afraid because we run….
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Peripheral Feedback Theory Each feeling has its own unique pattern
of emotional expression or bodily signature These are controlled by descending
pathways Feedback from these peripheral
responses onto the sensory cortex produces the conscious feeling
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Central Theory In 1920 two Neuroscientists, Cannon & Bard, established:
There is a maintenance of emotional responses after total removal of the cerebral cortices
This disproved the peripheral feedback theory That is to say the cortex is not necessary for expression of patterns of emotional
responses
Complete transection of above the hypothalamus: Found animal was still capable of expressing rage response Termed “sham rage”
Due to lack of input from cortical regions
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Central Theory Proposed central theory for
emotional expression Sensory info processed at
thalamus and sent to: Hypothalamus
Emotional responses Cortex
Conscious feelings
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Papez-Circuit
In 1937 James Papez came up with his own theory: For the most part agreed with the Cannon/Bard
central theory However suggested the presence of intermediate
structures between the hypothalamus & cerebral cortex
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Papez Circuit Thalamus relays signals to:
Sensory cortex Projects to cingulate cortex and Hippocampus
Projects back to hypothalamus Hypothalamus
Projects back onto anterior thalamic nuclei (ATN) ATN project to cingulate cortex
Convergence of signals at the cingulate cortex accounts for the conscious experience of feelings
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Papez Circuit
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Hippocampus-Overview An elaboration of the cerebral cortex
Situated in the medial temporal lobe Cortex narrows into single layer of densely packed
pyramidal neurons Area of the brain where long term potentiation (LTP) was
first identified
Acts as a storage site for memories
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Hippocampus-Structure
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Hippocampus-Structure
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Hippocampus-Parahippocampal Structures
Parahippocampal gyrus Entorhinal cortex
Network for memory & spatial navigation Interface between hippocampus & neocortex Projects via perforant pathways
Direct Indirect
Perirhinal cortex Visual recognition of of complex objects Connections to all major sensory areas
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Hippocampus-Perforant Pathways
Direct pathway Projects directly to CA1 neurons in hippocampus Involved in consolidation
Conversion of short term memories into long term memories
Indirect pathway Projects to granule cells in dentate Granule cells project to CA3 region
Via mossy fiber pathways CA3 neurons project to CA1 neurons
Via Schaffer collaterals Indirect pathway is involved in complex spatial learning & memory
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Hippocampus-Projections CA1 back to parahippocampal gyrus
From here to neocortex
CA1 to left & right fornices Mammillary bodies (part of hypothalamus)
Mammillothalamic tracts Anterior thalamic nuclei
Neocortex
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Long Term Potentiation (LTP) What exactly is LTP?
Long lasting increase in the amplitude of EPSP’s Achieved by a tetanus (train of stimuli)
Similar forms of potentiation have been described in fear conditioning (amygdala)
Seen at all 3 synapses in hippocampus Lasts days to weeks Does not induce a single form of plasticity, either alters:
Presynaptic cell (Altering NT release) Postsynaptic cell (Altering NT sensitivity; formation of new synapses) Both
Kandel ER, Schwartz JH, Jessell TM 2000. Principles of Neural Science, 5th ed. McGraw-Hill, New York
Long Term Potentiation Non-associative LTP
Occurs at mossy fiber pathway Presynaptic process
Increases neurotransmitter release via Ca2+ mediated recruitment of vesicles & closure of K+ channels
Associative LTP Occurs in Schaffer collateral pathway Both pre & postsynaptic process
Mediated by calcium/calmodulin complex