The Diencephalon, Cerebrum, and Cerebral Cortex

The diencephalon links

the midbrain to the cerebrum

The diencephalon is home to

the thalamus and hypothalamus

Thalamus (arguably) should be known as

thalami

The thalamus is not truly __, but a ___

not truly a single structure, but a composite of nuclei

Thalamus Functions

1. An active gatekeeper for sensory information

2. Key component for motor-related circuits

3. Regulating signals related to emotion, memory and autonomic control

How is the thalamus an active gatekeeper for sensory information?

• It transmits from the spinal cord and brainstem → to perceptual processing regions of the cerebral cortex.

• All of the senses except for smell

• Sometimes simply passing information along, other times:

  • Modifying incoming sensory information

  • Influencing attentiveness of cerebral cortex to specific sensory information

How is the thalamus a key component for motor-related circuits?

• Learning complex actions and skills

• Selecting appropriate response to meet situational goals

• Refining motor movements so they are smooth and automatic

The thalamus regulates signals related to:

emotion, memory and autonomic control

Damage to the Thalamus may result in

Wernicke’s Encephalopathy and Korsakoff Syndrome. Although rare, it can also be associated with hearing loss.

Hypothalamus

Also includes multiple nuclei, Regulates and maintains the body’s homeostasis within an optimal physiological range

Hypothalamus functions

• Regulates autonomic motor and sensory processes, as well as endocrine processes

  • Body growth

  • Temperature control

  • Reproduction

  • Fluid and electrolyte balance

  • Circadian rhythm regulation

  • Management of metabolic energy intake and expenditure

• Massive integrator of information that

  • Gauges the nature of the body within an environmental context and

  • Creates a general automatic behavioral response

• Able to initiate appropriate motor responses to internal or external conditions

• Hormone secretion

  • Hypothalamus activates the pituitary gland

  • Pituitary gland secretes hormones

  • Hypothalamus detects concentration of hormones and then adjusts its own activity and pituitary gland activity

Prader-Willi Syndorme

• Example of what could happen if hypothalamus is damaged

• Difficulties related to the hypothalamus (and pituitary glands)

  • Hyperphagia

  • Growth hormone deficiencies

  • Thyroid disorders

Cerebrum

• Split into two symmetrical regions called the cerebral hemispheres by the longitudinal cerebral fissure

• Hemispheres are joined together via corpus callosum

Cerebral Cortex

• Cortex primarily

  • Analyzes incoming sensations

  • Forms predictions about the world

  • Orchestrates the activity of the rest of the CNS

• Is adaptive, facilitating neuroplasticity

Cerebrum and Cerebral Cortex

• Each cerebral hemisphere consists of four lobes

  • Frontal, parietal, occipital, and temporal lobes

• Possesses characteristic grooves and ridges, called sulci and gyri

  • Can orient self using the central sulcus and lateral sulcus

Frontal Lobe

• Center for cognition and motor control

• Integrating signals from the rest of the brain

Frontal Lobe: Primary Motor Cortex (M1)

• Precentral gyrus

• Origin point for descending motor pathways

• Stimulation of M1 neurons produces:

  • Contraction of discrete muscles in the body

  • Fragments of coordinated and purposeful actions

• M1 is somatotopically organized

• Hub for inputs from the cerebellum, basal ganglia and the pre-motor area

• Obtains somatosensory inputs from the thalamus and from the primary somatosensory cortex

Case Study 1: A 23 year old man reports to physician due to shoulder weakness and instability. His left shoulder appears to reside lower than his right shoulder

CN XI- Accessory

Case Study 2: A 56 year old woman has been recovering from a traumatic brain injury, and many of her symptoms have resolved. However, since the injury, she consistently feels dehydrated and light headed no matter how much water she drinks. She also goes to the bathroom several times a day. During a follow up visit with her doctor, she learns that she has an issue with the hormone that helps her kidneys control the amount of fluid in her body. Which part of the nervous system is likely damaged and why?

hypothalamus

Case Study 3: A 47-year-old woman with a history of multiple sclerosis comes to her doctor complaining of sudden bursts of pain in her mandible, especially in the lower lip and cheek on her right side. This debilitating pain is often triggered by eating, talking, or brushing her teeth and often gets worse as the day progresses. Which part of the nervous system is likely damaged and why?

CV V- Trigeminal

Case Study 4: A 42-year-old man is brought to the hospital after a fall. The doctors identify that his lower legs are paralyzed. In addition, the man reports numbness and tingling in his lower legs. The remainder of the exam shows no further neurological signs or symptoms. Which part of the nervous system is likely damaged and why?

spinal cord

LEARN HOW TO DRAW CEREBRAL CORTEX AND COMPONENTS

EXTRA CREDIT → LOCATE THE MAJOR SULCI AND GYRI

Frontal Lobe: Premotor Cortex

• Divided into:

  • Pre-motor area (PMA)

  • Supplementary motor area (SMA)

• Active during the development and planning of actions

• PMA: Mostly planning actions of the limbs, responsive to visual inputs

• SMA: Planning of sequential actions based on level of complexity

Damage to Premotor Areas

Damage to premotor areas of the brain can result in apraxias

• including apraxia of speech, but also others

Frontal Lobe: Broca’s Area

• Believed to coordinate interactions between speech-related zones of the temporal lobe

• Especially plays a role in:

  • Language production

  • Semantic processing

  • Selection of competing semantic interpretations

• Pure damage to Broca’s area is rare

__ damage to Broca’s area is rare

Pure

Pure damage to __ area is rare

Broca’s

Broca’s area especially plays a role in:

• language production

• semantic processing

• selection of competing semantic interpretations

What is believed to coordinate interactions between speech-related zones of the temporal lobe?

Broca’s area

What is Broca’s area believed to coordinate?

interactions between speech-related zones of the temporal lobe

What plays a role in language production?

Broca’s area

What plays a role in semantic processing?

Broca’s area

What plays a role in the selection of competing semantic interpretations?

Broca’s area

Damage to (and Directly Around) Broca’s Area

• Broca’s-like aphasia

  • Relatively expressive aphasia

  • Impaired expressive production

  • Relatively intact comprehension

Broca’s-like aphasia

• Relatively expressive aphasia

• Impaired expressive production

• Relatively intact comprehension

Frontal Lobe: Prefrontal Cortex

• Executive functions:

  • Judgement

  • Future planning

  • Sense of purpose in an action

  • Notion of personal responsibility

  • Adherence to social norms and constructs

• Interconnections with several brain regions

What are examples of executive functions?

Judgement, Future planning, Sense of purpose in an action, Notion of personal responsibility, Adherence to social norms and constructs

What part of the frontal lobe is involved in executive functions?

prefrontal cortex

What part of the brain is involved in executive functions?

frontal lobe: prefrontal cortex

What part of the brain is responsible for executive functions such as judgement, future planning, sense of purpose in an action, notion or personal responsibility and adherence to social norms and constructs?

frontal lobe: prefrontal cortex

What part of the frontal lobe is involved in executive functions such as judgement, future planning, sense of purpose in an action, notion of personal responsibility and adherence to social norms and constructs?

prefrontal cortex

Parietal Lobe

• Critical region for being able to detect and discriminate all forms of somatic inputs

• Operates as the sensory complement to motor performance

somatic

touch, sensation, pain and temperature

What is the critical region for being able to detect and discriminate all forms of somatic inputs?

Parietal Lobe

What operates as the sensory complement to motor performance?

Parietal Lobe

What is the parietal lobe the critical region for?

being able to detect and discriminate all forms of somatic inputs

What does the parietal lobe operate as?

the sensory complement to motor performance

Parietal Lobe: Primary Somatosensory Cortex (S1)

• Cortical receptive site for sensory inputs from the periphery related to:

  • Touch

  • Proprioception

  • Noxious and thermal sensations

• Has a somatotopic representation of the body’s sensory surfaces

Parietal Lobe S1

Primary Somatosensory Cortex (S1)

What has a somatotopic representation of the body’s sensory surfaces?

Parietal Lobe: Primary Somatosensory Cortex (S1)

What does the Parietal Lobe: Primary Somatosensory Cortex (S1) have?

a somatotopic representation of the body’s sensory surfaces

What is the cortical receptive site for sensory inputs from the periphery related to touch, proprioception and noxious and thermal sensations?

Parietal Lobe: Primary Somatosensory Cortex (S1)

Proprioception

the sense that lets us perceive the location, movement and action of parts of the body. This includes perception of joint position and movement, muscle force and effort

Parietal Lobe: Association Areas

• Superior parietal lobule

  • Active during the direction of attention and the interpretation of visual and spatial when observing an object

• Inferior parietal lobe

  • Supramarginal gyrus

    • Important for the phonological mechanism of verbal working memory

  • Angular gyrus

    • Important for semantic processing

What are the association areas in the parietal lobe?

Superior parietal lobule, Inferior parietal lobe and within the inferior parietal lobe there is the supramarginal gyrus and angular gyrus

Superior parietal lobule

Active during the direction of attention and the interpretation of visual and spatial when observing an object

Inferior Parietal Lobe

composed of the supramarginal gyrus (important for the phonological mechanism of the verbal working memory) and the angular gyrus (important for semantic processing)

Supramarginal gyrus

Important for the phonological mechanism of verbal working memory

Angular gyrus

Important for semantic processing

What is active during the direction of attention and the interpretation of visual and spatial when observing an object?

superior parietal lobule

What is important for the phonological mechanism of verbal working memory?

the supramarginal gyrus in the inferior parietal lobe

What is important for semantic processing?

the angular gyrus within the inferior parietal lobe

Precuneus

• located on medial wall of cerebrum

• Thought to comprise a central region of a critical brain system that is active at rest: default-mode network

• Important for memory and consciousness

Temporal Lobe

• Home of auditory and language comprehension neural circuits

• Key cerebral region involved in memory and for the identification and representation of complex objects

Temporal Lobe: Primary Auditory Cortex (A1)

• Main input site for auditory inputs

• Refers to the gyrus within (red structure in bottom image)

• Has tonotopic mapping of sound inputs reflecting frequency responsiveness of cochlea

• Also organized for more complex acoustic relationships

What has tonotopic mapping of sound inputs reflecting frequency responsiveness of cochlea?

temporal lobe: primary auditory cortex

What is organized for more complex acoustic relationships?

temporal lobe: primary auditory cortex

Cortical Deafness

• While extremely rare (12 reported cases), it is possible for a lesion in the brain to lead to cortical deafness, which is associated with absence of hearing for all sounds (speech and non-speech)

• In These cases, the brain cannot process sound

• Since traditional hearing aids work by amplifying sound, how do you think hearing aids would impact someone with cortical deafness? Why?

Would hearing aids help people with cortical deafness?

No, because amplifying sound does not change the fact that someone with cortical deafness cannot process sound

Temporal Lobe: Wernicke’s Area

• hub for language reception and comprehension

• Exact location is not well-defined

What is the hub for language reception and comprehension?

temporal love: wernicke’s area

Wernicke’s exact location is

not well-defined

Damage to (and directly around) Wernicke’s Area

• Wernicke’s-like aphasia

  • Relatively receptive aphasia

  • Impaired language comprehension

  • Relatively intact expressive language in terms of form

  • Expressive language will typically show impacts through word choises that do not make sense

Wernicke’s-like aphasia is a relatively ___ aphasia

receptive

This type of aphasia results in impaired language comprehension but relatively intact expressive language in terms of form

Wernicke’s aphasia

In Wernicke’s-like aphasia, expressive language will typically show impacts through

word choices that do not make sense

Temporal Lobe: Association Areas

• Receives heavy inputs form visual cortices related to form, shape, size, and texture

• Other inputs include language-related information from Wernicke’s area and surrounding auditory association zones

• Medial most region for learning, memory, and emotional regulation

Occipital Lobe

• Separate out visual stream into smaller inputs

• Features are re-composed and are output to either the parietal or temporal areas of the cerebrum for integration

• Includes primary visual cortex (V1)

Insula

• Known activity in sensory perception, pain management, emotional reactions such as fear and anxiety, motor control, language, speech production, decision-making, body awareness, swallowing, pain perception

• Thought to represent a processing hub

Parallel Processing

• Not simply hierarchical processing

• Parallel processing is ability of nervous system to simultaneously manage different parts of a single complex experience at once

Mapping the Cerebral Cortex

• Brodmann’s Map

• Lateral and Medial Cortex

• “Gold standard” classification system

The lateral fissure separates which lobe from the frontal lobe?

• Occipital

• Parietal

• Temporal

Temporal. The lateral fissure separates the temporal lobe from the frontal and parietal lobes.

Damage in the parietal lobe would be most likely to cause which dysfunction?

Loss of touch. The primary somatosensory cortex is located in the parietal lobe

Loss of motor control can be attributed to damage to which lobe?

frontal lobe

Difficulty with critical thinking can be attributed to damage in which lobe?

frontal lobe

Loss of memory can be attributed to damage in which lobe?

temporal lobe

The precentral gyrus (primary motor cortex) is located in which lobe?

frontal lobe

The brainstem is __ to the parietal lobe

ventral

The frontal lobe is __ to the occipital lobe

rostral

The Limbic System

• Interconnected nervous system components that are central to:

  • Learning and memory

  • Emotional processing

  • Instinctual regulation

• The major or core structures that comprise the limbic system include

  • Hippocampus

  • Amygdala

  • Cingulate

  • Hypothalamus

  • Septal nuclei

What is the limbic system?

Interconnected nervous system components that are central to learning and memory, emotional processing and instinctual regulation

The major or core structures that comprise the limbic system include

hippocampus, amygdala, Cingulate, hypothalamus, Septai nuclei

Limbic System Functioning as a Whole

• Using emotions associated with an experience to drive our brain to engage with and remember events

• The importance of emotionally powerful responses

• Serves to select and filter what information people engage with and remember

• We are not proposing that the limbic system houses the entirety of emotional of memory functioning

The Hippocampus/Hippocampal Formation

• Highly active during different phases of conditioning and associative learning

• Important in the development of spatial learning skills

• Consolidating newly learned factual and event-related memories and transferring them into long-term storage

• Ruffled appearance

• Uses connections to several structures to quickly adapt and reacts