Papez Circuit Flashcards Preview

Functional neuro > Papez Circuit > Flashcards

Flashcards in Papez Circuit Deck (19)
Loading flashcards...
1
Q

Papez circuit

A

The structures of the Papez circuit in the brain form a limbus shape around the brainstem.

2
Q

Papez circuit

A

The Papez circuit is a neural pathway in the brain first described by American neuroanatomist James Papez in 1937. Papez believed that the circuit was involved with emotions.

3
Q

Papez circuit

A

Recent studies show that it has a more significant role in memory functions than in emotions. The Papez circuit was later modified by American neuroscientist and physician Paul D. MacLean and now, the circuit is known as the limbic system. Damage to parts of the Papez circuit have shed light on not only its function, but on possible diagnosis of many disorders relating to memory.

4
Q

Papez circuit

A

Neuroscientist Paul D. MacLean is famous for his work on the limbic system and its evolutionary history.

5
Q

Papez circuit

A

In 1907/1908, Bavarian neuropathologist Christfried Jakob discovered the visceral brain. By date, he held the “… first interpretation of the limbic or ‘internal’ brain as a viscero-emotional mechanism…” He traced the structures of the system based on degeneration experiments in apes and dogs as well as neurodegenerative diseases in humans

6
Q

Papez circuit

A

it was not until 1937 when James Papez studied this system in detail that it became famous. Papez had been studying cases of rabies which is a disease that causes high levels of aggression. He noticed that this heightened aggression correlated with damage to the hippocampus.[2] Theoretically, this made sense to Papez who asserted that the hippocampus is responsible for the expression of emotion because of its connection to the autonomic nervous system. He also noticed that in other cases, certain stimuli (taste, smell, pain, etc.) would cause strong emotional responses. These stimuli activated not only the hippocampus but also other brain structures. He theorized that these brain structures worked together as the emotional control center in the brain and consequently founded the Papez circuit.[3] Because of these studies, Papez strongly believed that the circuit was the cortical control of emotion.

7
Q

Papez circuit

A

Paul D. MacLean was also interested in the Papez circuit. He had read through Paul Broca’s research which indicated that the limbic lobe that surrounds the brainstem is a structure present in all mammals. Papez’s paper on the emotional circuit which involved the connection between the hypothalamus and the limbic lobe set MacLean on a journey to learn more. He visited Papez at Cornell University after which he proposed a modified version of the Papez circuit in 1952, emphasizing not only the hippocampus, but also the amygdala and septum

8
Q

Papez circuit

A

The hippocampus, amygdala, and septum make up the rhinencephalon (frontotemporal portion of the brain) or, as Jakob termed it, the visceral brain. Together, the limbic lobe and the visceral brain make up the limbic system. MacLean believed that including the visceral brain in the limbic system accounted for the external sensory information associated with subjective emotional experiences. Since the limbic system consists of evolutionary primitive structures which prevents its interpretation verbally, the visceral brain accounts for the visual, auditory, olfactory, and other external sensory inputs that are associated with emotions

9
Q

Papez circuit

A

Recently, many studies have been done to analyze the anatomy and function of the Papez circuit. Many scientists have been finding proof that the circuit is related to memory as well as emotion. The limbic system, the modified version of the circuit proposed by MacLean, is thought to be involved in the same functions as well as behavior, motivation, and olfaction

10
Q

Papez circuit

Emotion

A

Based on Papez’s experiment with aggression in rats and other studies, it was initially believed that the circuit was involved with emotion. The circuit connects the hypothalamus and the cortex and acts as the emotional system of the brain. “The cingulate cortex projects to the hippocampus, and the hippocampus projects to the hypothalamus by way of the bundle of axons called the fornix. Hypothalamic effects reach the cortex via a relay in the anterior thalamic nuclei.”

11
Q

Papez circuit

Emotion

A

However, there has not been additional proof of the circuit’s role in emotion over the years. Now, the amygdala is thought to play a key role in emotion, a structure that was not a part of the Papez circuit until 1952 when MacLean included it in the modified version of the circuit, the limbic system.

12
Q

Papez circuit

Memory

A

In the past few years, many experiments have been done that involve structures of the Papez circuit. Moreover, many cases where structures of the Papez circuit have been damaged show changes that indicate its real function.

13
Q

Papez circuit

Memory

A

Theta waves are used to measure activity in mainly the hippocampus but can be used to measure other brain regions as well. Strong synchronization of theta waves in the hippocampus and anterior ventral thalamus has been observed. Although theta waves between the hippocampus and the anterior dorsal and anterior medial regions in the thalamus showed no synchronization, scientists have seen a marked increase in firing rates of the neurons in the brain regions.[9] Overall, based on theta wave experimentation, some components of the Papez circuit have shown to indeed have a connection and work together. Also, theta waves are thought to be linked to learning and memory. Consequently, many scientists believe that the Papez circuit is involved with memory because of theta wave experiments. Some scientists have narrowed it down to specifically spatial and episodic memory.

14
Q

Papez circuit

Memory

A

Damage to the mammillothalamic tract, ventral anterior nucleus, and ventral lateral nucleus can result in memory and language impairment.[12] Amnesia can be a result of disconnection of the mammillary bodies from the Papez circuit

15
Q

Papez circuit

Memory

A

The fornix is a bundle of nerve tracts made of white matter. It is crucial in normal cognitive functions. Harm to the fornix can result in amnesia.

16
Q

Alzheimer’s disease

A

is a common neurodegenerative disease and a form of dementia. It leaves patients impaired or unable to learn new information. They usually have difficulty coming with the names of people, objects, etc. Degeneration or other neural problems because of this disease commonly occurs in parts of the Papez circuit. It is already known that problems with episodic memory are linked to tumors or damage in the Papez circuit. Specific structures of the Papez circuit linked to episodic memory are the hippocampus and other medial temporal lobe structures. As a result of these adverse effects on episodic memory, damage to the Papez circuit can not only indicate or predict amnesia but also Alzheimer’s in a patient

17
Q

Semantic dementia

A

Semantic dementia is a rare degenerative disorder that exhibits defects in all semantic memory functions, including naming, single word comprehension and impoverished general knowledge, with relative preservation of other components of speech, perceptual and nonverbal problem-solving skills, and episodic memory. This may occur due to damage in the mammillary bodies, ventral anterior nucleus, and ventral lateral nucleus which has resulted in disruption in language in previous research

18
Q

Korsakoff’s syndrome

A

occurs when a chronic alcoholic patient suffers from poor nutrition and specifically develops a thiamine deficiency. Usually with this disease, there are widespread abnormalities in the Papez and fronto-cerebellar circuits.[17] The mammillary bodies are an important part of the Papez circuit. If there is damage, such as loss of neurons and/or myelination, to the mammillary bodies, the Papez circuit can be severely affected. There will be a disruption in the connecting parts of the system. As a result, the ability to learn new information or to retrieve recently acquired memories is significantly reduced or lost.

19
Q

Transient global amnesia

A

is a very rare disorder and not much is known about it. Patients acutely develop a selective disorder of episodic memory, losing from several to 48 hours of previously learned information and are unable to learn new information. Damage to the hippocampus and other medial lobe structures in the Papez circuit is thought to be the cause of reduced or lost episodic memory