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[[File:Papez Circuit.jpg|thumb|right|400px|Papez Circuit]]

The Papez circuit, first discovered by James Papez in 1937, is a loop that consolidates memories into the long-term store. This loop runs from the association cortex to the [[cingulate gyrus]] and [[hippocampal formation]] onto the [[amygdala]] and [[mammillary bodies]], via the [[fornix]]; then onto the [[hypothalamus]]; from the [[mammillary bodies]] to the [[anterior thalamic nuclei]] via the [[mammillo thalamic tract]]; back to the cingulate gyrus and the prefrontal cortex.
It is more commonly associated with [[declarative memory]] rather than [[procedural memory]]. Damage to the Papez circuit will lead to insufficient [[consolidation]] of memories, and can lead to memory disorders. These include: [[retrograde]] and [[anterograde amnesia]]; [[Alzheimer’s]]; [[Korsakoff’s syndrome]]; and [[Kluver-Bucy syndrome]].


==Function of the Papez circuit==
==Function of the Papez circuit==
The Papez circuits’ role is to consolidate and retrieve long-term memories. Disruption to any part of the Papez circuit in the form of damage or scarring can cause deficits in [[declarative memory]]. <ref> Carlesimo, G. G., Lombardi, M. G., & Caltagirone, C. (2011) Vascular -Thalamic Amnesia: A Reappraisal, ''Neuropsychologia'' ''49''(5) 777-789. </ref>
The Papez circuits’ role is to consolidate and retrieve long-term memories. Disruption to any part of the Papez circuit in the form of damage or scarring can cause deficits in [[declarative memory]]. <ref> Carlesimo, G. G., Lombardi, M. G., & Caltagirone, C. (2011) Vascular -Thalamic Amnesia: A Reappraisal, ''Neuropsychologia'' ''49''(5) 777-789. </ref>

Revision as of 11:12, 15 November 2012

Papez Circuit

The Papez circuit, first discovered by James Papez in 1937, is a loop that consolidates memories into the long-term store. This loop runs from the association cortex to the cingulate gyrus and hippocampal formation onto the amygdala and mammillary bodies, via the fornix; then onto the hypothalamus; from the mammillary bodies to the anterior thalamic nuclei via the mammillo thalamic tract; back to the cingulate gyrus and the prefrontal cortex. It is more commonly associated with declarative memory rather than procedural memory. Damage to the Papez circuit will lead to insufficient consolidation of memories, and can lead to memory disorders. These include: retrograde and anterograde amnesia; Alzheimer’s; Korsakoff’s syndrome; and Kluver-Bucy syndrome.


Function of the Papez circuit

The Papez circuits’ role is to consolidate and retrieve long-term memories. Disruption to any part of the Papez circuit in the form of damage or scarring can cause deficits in declarative memory. [1]

Consolidation of Long Term Memory

Long term memory is divided into two types of memory: declarative and procedural. Procedural memory refers to unconscious memories such as priming, simple forms of conditioning, skills and habits [2] . The mechanisms involved in procedural memory are not thought to be contingent with the Papez circuit. Declarative memory refers to conscious recall of facts (semantic memories) and events (episodic memory) [3]. [4]. Findings with amnesic patients who have suffered damaged to the Papez circuit, such as HM have shown to have intact procedural memory, but impaired declarative memory. [See section 6.1.2 and 6.1.3]

The Papez circuit can be imagined as the ‘glue’ that holds memories together. For example, when you first see a face and hear a name at the same time, the Papez circuit will consolidate those two pieces of information (i.e., auditory and visual) together. This is stored in long term memory. Repeated exposure to both stimuli, will lead to a fully consolidated memory. Note that long-term memories are not stored within the structures of the Papez circuit, they are simply retrieved from their original storage through the mechanisms of the Papez circuit (see figure 4). Damage to the Papez circuit will result in insufficient consolidation, therefore not allowing the memory to be transferred to the long term store. Research suggests that fully consolidated memories no longer rely on the Papez circuit. [5] These conclusions are heavily based on research with amnesic patients [6] (see section 6.2)

Amnesia

There are two types of amnesia: anterograde (See anterograde amnesia and retrograde. Anterograde amnesia is where a person is unable to remember on going events after a head trauma. A sufferer of anterograde amnesia will not tend to forget who they are, or anything previous to the incident; however they will have severe difficulty remembering anything new. Retrograde amnesia is where a person is able to remember things after an incident, but will not remember things previous to the event. This retrograde effect has been reported to span over some years before the brain trauma. However older memories are in some cases spared. Leading to the theory that consolidation over a long period of time will result in fully consolidated memories that are no longer dependent on the Papez circuit (in particular the hippocampus). [7] [8]

Damage to different components of the Papez circuit is thought to lead to different forms of memory impairment. (See table 1)

Area with Damage Resulting Effect
Hippocampal Formation Bilateral damage causes anterograde and in some case retrograde amnesia [9]
Fornix Can cause impairments of temporal order memory for retrograde information [10]
Mammillary Bodies Korsakoff’s Syndrome; Anterograde Amnesia [11]
Mamillothalamic tract Markedly impaired declarative memory (both anterograde and retrograde amnesia); linked with Korsakoff’s Syndrome [12]
Anterior Thalamic Nuclei Linked to Korskaoff’s syndrome; spatial memory deficits. [13]
Cingulate Gyrus Schizophrenia; disorientation as a major component of dementia [14]
Amygdala Klüver-Bucy syndrome (visual agnosia) [15]
Hypothalamus Anterograde and to a lesser extent retrograde amnesia; verbal memory impairment (Patient B.J) [16]
Prefrontal Cortex Spatial memory deficit; Working memory deficits [17]
Association Cortex Working memory deficits [18]

H.M.

In 1953, Patient H.M. underwent surgery to treat his epilepsy. The surgery consisted of bilateral removal of his medial temporal lobe (including the hippocampal formation and amygdala). As a direct result of this procedure H.M’s seizures decreased significantly, but more prominent was the severe anterograde amnesia that persisted. H.M showed impaired declarative memory functions for both forming new memories (anterograde amnesia) and retrieving old memories (retrograde amnesia). However the retrograde effect appeared to be on a time gradient, very old memories remained intact. Nondeclarative forms of memory appeared to be intact (i.e. priming tasks). From the hundreds of studies that H.M participated in, the general consensus implicates the medial temporal lobe as essential for the formation and temporal storage of memories, until fully consolidated. [19] [20]

Alzheimer’s

Alzheimer’s disease (AD) is a progressive neurodegenerative disease. Neuronal degeneration in AD begins in the medial temporal lobe structures, including the entorhinal cortex and hippocampus. Further neuroanotomic spread then incorporates other critical components of the Papez circuit, including the amygdala and anterior cingulate; which leads to the behavioural characteristics of AD. Eventually this spreads to involve the frontal regions, finally leading to death. AD is characterised by many symptoms, the most common being long-term memory loss, trouble with language, and confusion. [21]


Korsakoff’s Syndrome

Korsakoff's syndrome is characterised by deficits in declarative memory, both anterograde and retrograde amnesia, confabulations and has also been linked with temporal order deficits. [22] Korsakoff’s syndrome is caused by damage to the medial thalamus and hypothalamus, in particular the mammillary bodies. [23] The most common cause of Korsakoff’s syndrome is a thiamine (vitamin B1) deficiency, through alcoholism or malnutrition. [24]

Klüver-Bucy Syndrome

Paul Bucy and Heinrich Klüver demonstrated that disrupting the Papez circuit by damage to the amygdala leads to profound effects on social and emotional behaviour. Klüver-Bucy syndrome is recognised by a combination of visual agnosia, placidity, hyperorality and hypersexuality. Visual agnosia is an inability to recognise objects or faces, and can lead to other memory disorders. [25]

References

  1. ^ Carlesimo, G. G., Lombardi, M. G., & Caltagirone, C. (2011) Vascular -Thalamic Amnesia: A Reappraisal, Neuropsychologia 49(5) 777-789.
  2. ^ Alvarez, P., & Squire, L. R., (1994) Memory consolidation and the medial temporal lobe, a simple network model. PNAS 91(15) 7041-7045
  3. ^ Tulving, E., & Markowitsch, H. J., (1998) Episodic and declarative memory: role of the hippocampus Hippocampus 8(3) 198-204
  4. ^ Tulving, E., (2002) Episodic Memory: from mind to brain, Annual Review of Psychology 53 1-25
  5. ^ Nadel, L., & Bohbot, V. (2001) Consolidation of Memory. Hippocampus 11(1) 56-60
  6. ^ Carlesimo, G.A., (2012) Memory Disorders in Patients with Cerebral Tumours Journal of Neuro-oncology 108(2) 253-256
  7. ^ MedicineNet(2012) Definition on Retrograde Amnesia. Retrived from: http://www.medterms.com/script/main/art.asp?articlekey=11959
  8. ^ Markowitsch, H. J., (2005) The neuroanatomy of memory. In Halligan, P.W., & Wade, T. D. (Eds.), Effectiveness of Rehabilitation for Cognitive Deficits 105-110. Oxford, England: Oxford University Press.
  9. ^ Zola-Morgan, S., Squire, L. R., & Amaral, D. G. (1989) Lesions of the hippocampal formation but not lesions of the fornix or the mammillary nuclei produce long-lasting memory impairment in monkeys. The Journal of Neuroscience 9 (3) 898-913
  10. ^ Yasuno, F., Hirati, M., Takimoto, H., Taniguchi, M., Nakagawa, Y., Ikekiri, Y … Takeda, M. (1999). Retrograde temporal order amnesia resulting from damage to the fornix. Journal of Neurology, Neurosurgery and Psychiatry, 67, 102-105.
  11. ^ Tanaka, Y., Miyazawa, Y., Akaoka, F., & Yamada, T. (1997) Amnesia Following Damage to the Mammillary Bodies Neurology 481) 160-165
  12. ^ Gold, J, J., & Squire, L. R. (2006) The anatomy of amnesia: Neurohistological analysis of three new cases. Learning and Memory 13 699-710
  13. ^ Harding, A., Halliday, G., Caine, D., & Kril, J. (1999) Degeneration of anterior thalamic nuclei differentiates alcoholics with amnesia. Brain 123(1) 141-154
  14. ^ Benes, F. M., Sorensen, I., Vincent, S. L., Bird, E. D., & Sathi, M. (1992) Increased Density of Glutamate-immunoreactive Vertical Processes in Superficial Lamina in Cingulaye Cortex of Schizophrenic Brain. Cerebral Cortex 2(6) 503-512
  15. ^ Hayman, L. A., Rexer, J. L., Pavol, M. A., Strite, D., & Meyers, C. A. (1998) Kluver-Bucy Syndrome After Bilateral Selective Damage of Amygdala and Its Cortical Connections The Journal of Neuropsychiatry and Clinical Neurosciences 10 354-358
  16. ^ Dusoir, H., Kapur, N., Byrnes, D. P., McKinstry, S., Hoare, R. D. (1989) Human Memory Disorder: Evidence from a penetrating paranasal brain injury. Brain 113(6) 1695-1706
  17. ^ McCarthy, G., Blamire, A. M., Puce, A., Nobre, A. C., Bloch, G., Hyder, F., … Shulman, R. G. (1994) Functional magnetic resonance imaging of human prefrontal cortex activation during a spatial working memory task. PNAS 91(18) 8690-8694
  18. ^ Colombo, M., D’Amato, M. R., Rodman, H. R., & Gross, C. G. (1990) Auditory Association Cortex Lesions Impair Audiory Short-Term Memory in Monkeys. Science 247 336-338
  19. ^ Corkin, S. (2002) What’s new with the amnesic patient H.M. Nature 3 153-160
  20. ^ Scoville, W. B., & Milner, B. (1957) Loss of recent memory after bilateral hippocampal lesions ‘’Journal of Neurology, Neurosurgery, Psychiatry’’ ‘’20’’(11) 11-21
  21. ^ Jicha, G. A., & Carr, S. A. (2010) Conceptual Evolution in Alzheimer’s disease: Implications for understanding the clinical phenotype of progressive neurodegenerative disease. Journal of Alzheimer’s Disease 19(1) 253-272
  22. ^ Shimamura, A. P., Janowsky, J. S., & Squire, L. R. (1990) Memory for the temporal order of events in patients with frontal love lesions and amnesic patients. Neuropsychologia 28(8) 803-813
  23. ^ Shimamura, A.P., Jernigan, T. L., & Squire, L. R. (1988) Korsakoff’s syndrome: radiology (CT) findings and neuropsychological correlates. Journal of Neuroscience 8(11) 4400-4410
  24. ^ Alzheimer’s Society (2012) What is Korsakoff’s Syndrome. Retrieved from http://www.alzheimers.org.uk/site/scripts/documents_info.php?documentID=98
  25. ^ Hooshmand, H., Sepdham, T., & Vries, J. K. (1974) Kluver-Bucy Syndrome: Successful Treatment with Carbamazepine. JAMA 229(13)
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