prefrontal cortex

Question 1

Describe the development of the prefrontal cortex?

Answer 1

• first two years cell volume grows rapidly - neuronal length, branching and cell volume
• lot of grey matter from the first two years, minimal white matter
• synaptic density stabilises around 16 years
• neurotransmitter levels reach peak in early adulthood
• prefrontal cortex is not fully developed until 30 years old

Question 2

Describe the prefrontal cortex in relation to other species.

Answer 2

• larger prefrontal cortex as a percentage of total cortex
• more prefrontal cortex white matter

Question 3

Name the three main functional units (and subunits), and the associated unit of the PFC.

Answer 3

Medial - dorsomedial and ventromedial
Lateral - dorsolateral and venrolateral
Orbital
Anterior cingulate cortex - associated due to a few shared functions, however it is considered more to be a part of the limbic system

Question 4

How many layers of the PFC are there? Name them.
Which layers are inhibitory or excitatory, or both? Why?

Answer 4

6 Layers ->
- molecular layer
- external granular
- external pyramidal
- internal granular
- internal pyramidal
- multiform/ polymorphic layer

Pyramidal are excitatory
Granular layers are both inhibitory and excitatory - they contain interneurons, which are inhibitory, as well as excitatory pyramidal neurons

Question 5

Which layer of the PFC receives and sends signals primarily to the thalamus?

Answer 5

Layer 4 - internal granular layer

Question 6

Which layers receive information from cortical areas (excluding the thalamus)?

Answer 6

Layers 1, 2, 3, 5

Question 7

From which thalamic nuclei does the PFC receive the majority of it’s projections from? What are the other two nuclei?

Answer 7

Majority (80%) from mediodorsal thalamic nuclei. Other afferent projections from ventral anterior and anterior thalamic nuclei.

Question 8

What are the four neuromodulatory inputs in the PFC? Where do they originate from?

Answer 8

Acetylcholine - released from basal forebrain
Dopamine - released from ventral tegmental area and substantia nigra compacta
Seratonin - released from dorsal raphe nuclei
Noradrenaline - released from locus coeruleus

Question 9

What is the overall function of the PFC?

Answer 9

• personality
• decision making
• planning of movement
• goal directed actions and behaviours
• memory
• emotional regulation
• attention
• sequenced behaviour
• social behaviour

Question 10

Describe what happened to Phineas Gage, and what the outcomes were?

Answer 10

Ventrolateral and medial PFC damage
Changes in initiative to complete activities, emotional regulation, social behaviour

Question 11

Describe what occurs in frontal lobotomies?

Answer 11

The white matter connections to the rest of the brain are severed, particularly connections from the thalamus.
Leads to lack of emotional responses, lack of motivation, listlessness, lack of interest

Question 12

What does the Wisconsin Card Sorting Test assess?

Answer 12

Assesses all major funtion of the PFC
-> tests rule switching, which is impaired in schizophrenia

Question 12

What is the primary function of the dorsolateral PFC?

Answer 12

Role in working memory, particularly visuospatial tasks
-> It is close to the enthorininal cortex and hippocampus!
It is found to be important in tasks in which you have to wait to relay information (delay between stimulus and response)

Question 13

Which area of the PFC is involved in working memory?

Answer 13

The dorsolateral PFC

Question 14

Which areas of the PFC are involved in emotional responses and memory?

Answer 14

The orbital frontal cortex, the ventromedial PFC and the anterior cingulate gyrus -> they form connections with the limbic structures

Question 15

Which areas of the PFC are involved in the fear response? Which areas correspond to which level of fear?

Answer 15

The ACC connects to the amygdala, and is responsible for high fear states
The ventromedial PFC connects to the amygdala, and is responsible for low fear states
These pathways are often impaired in people with PTSD

Question 16

What is Broca’s area responsible for? What does damage to this region cause?

Answer 16

Broca’s area (BA 44, 45) is responsible for the production of speech syntax -> damage to this region causes Broca’s aphasia

Question 17

Why did people think the PFC was the consciousness hub?

Answer 17

The PFC is responsible for many functions implicated in consciousness (attention, reasoning, memory, concept of self). However, the current belief of consciousness is taht consciousness involves all brain strcutures and the dense connectivity between them, not just the PFC