PM371 Encoding Part 1 & Language Cortical Areas - Lecture 3

Encoding Part 1: Association Cortices

• Presented by Prof Phil Newton, PM371 Learning, Memory and Cognition.

Encoding

• Key processes involved in encoding include:

  • Sensory Memory: Initial stage that holds sensory information briefly.

  • Short-term memory: Temporary storage system for holding limited information.

  • Attention: Focusing awareness on specific stimuli or aspects of the environment.

  • Working memory: Actively holding and manipulating information in mind.

  • Retrieval: Accessing and bringing stored information back into consciousness.

  • Learning: Acquiring new information or skills through experience, study, or being taught.

  • Long-term memory: Storage of information over an extended period.

  • Storage: Maintaining information in memory over time.

Ascending Sensory Pathway

• The ascending sensory pathway involves:

  • First-order neuron: Detects the stimulus at the periphery.

  • Second-order neuron (Spinothalamic tract): Transmits the signal from the spinal cord to the thalamus.

  • Third-order neuron (Thalamocortical projection): Projects the signal from the thalamus to the cortex.

  • The signal travels from the spinal cord to the thalamus and then to the cortex for processing.

Visual System Basics

• Visual information flow:

  • Left visual field projects to the right hemisphere, and vice versa, enabling contralateral processing.

  • Temporal retina receives information from the nasal visual field.

  • Nasal retina receives information from the temporal visual field, aiding in depth perception and spatial awareness.

  • Pathway: Eye -> Optic nerve -> Optic chiasma (where nasal retinal fibers cross) -> Lateral geniculate nucleus (LGN) in the thalamus -> Primary visual cortex (V1).

Cortical Lobes and Their Functions

• Frontal Cortex: Deals with "What do I do about it?" - higher-order cognitive processes, decision-making, and motor control.

• Parietal Cortex: Deals with "Where is it?" - spatial processing, attention, and sensory integration.

• Temporal Cortex: Deals with "What is it?" - object recognition, auditory processing, and memory.

• Occipital Cortex: Primarily involved in vision and visual processing.

Learning and Memory - Information Flow

• The flow of information in learning and memory involves several brain structures:

  • Sensory information enters through the thalamus, which acts as a relay station.

  • Cortical association areas process the information, integrating it with existing knowledge.

  • Parahippocampal and rhinal cortices are involved in the formation of new memories.

  • The hippocampus plays a crucial role in encoding new memories and spatial navigation.

  • The fornix connects the hippocampus to the mammillary bodies (hypothalamus), which are important for memory consolidation.

Neuroanatomy: Core Principles

• Key anatomical terms:

  • Cortex vs. Lobe: Cortex is the outer layer of the brain; lobes are divisions of the cortex.

  • Sulcus (plural: Sulci): A groove or furrow on the surface of the brain that increases surface area.

  • Gyrus (plural: Gyri): A ridge or fold between two clefts on the cerebral surface in the brain.

  

  • Brodmann Area: A region of the cortex defined by its cellular organization and function.

  • White Matter Tracts: Bundles of myelinated axons connecting different brain areas, facilitating communication.

  • Laterality: The specialization of function between the two hemispheres of the brain.

Sulci and Gyri

• Sulci are infoldings ('sulk') that increase the surface area of the cortex, allowing for more neurons to be packed into the brain.

• Gyri are the ridges between the sulci, forming the visible convolutions of the brain.

Key Sulci

• Central Sulcus: Separates the Parietal and Frontal Cortices, delineating motor and sensory areas.

• Lateral Sulcus (or Sylvian Fissure): Separates the Temporal Lobe from the Frontal and Parietal Lobes; important for auditory processing.

Insula (Insular Cortex)

• The insula is a region of the brain located deep within the lateral sulcus, involved in consciousness, emotion, and homeostasis.

Brodmann Areas

• Brodmann Areas: Map of the cortex based on histology (cellular structure), created by Korbinian Brodmann in 1909.

  • There are 52 regions, some subdivided, each associated with specific functions.

  • Still widely used today for localizing brain functions.

Examples of Brodmann Areas

• Primary Visual Cortex: Brodmann Area 17, responsible for initial visual processing.

• Fusiform Face Area: Part of Brodmann Area 37, involved in facial recognition.

Association Cortices

• Association cortices are not primary cortices; they integrate information from multiple sensory modalities and higher-order cognitive processes.

Posterior Parietal Cortex

• Function: Attending to stimuli; spatial awareness ("Where is it?").

• Brodmann areas: 5, 7, 39, 40.

• Important for attention, especially spatial attention, and integrates visual, auditory, and somatosensory information.

• Damage can result in "neglect", a condition where patients ignore one side of their visual field or body.

Hemineglect

• Hemineglect is a sign of posterior parietal cortex damage, characterized by neglect of one side of space or the body.

  • Sensory neglect: Ignoring incoming sensory information from the contralateral hemispace.

  • Conceptual neglect: Neglect of the body and external world in the contralateral hemifield.

  • Hemiasomatognosia: Patient denies that the affected side of the body belongs to them.

  • Motor neglect: Fewer movements in the contralateral space.

Temporal Cortex

• Function: Identifying the nature of stimuli ("What is it?") and processing auditory information, memory, and object recognition.

Agnosia

• Agnosia is the inability to recognize sensory stimuli, despite intact sensory processing.

Temporal Cortex Damage

• Inferior Temporal Cortex: Visual agnosia (“Psychic blindness”); patient can see but not identify objects.

  • Prosopagnosia (Face Blindness): Inability to recognize individuals from their faces; associated with the fusiform gyrus. Patients can describe facial parts but cannot identify the subject by voice or clothes.

• Middle Temporal Cortex: Movement agnosia; inability to distinguish between moving and stationary objects.

Integration of Sensory Streams

• Integration allows us to assemble a coherent perspective on the world, combining inputs from different senses to create a unified experience.

Consciousness

• The brain predicts a view of the world based on perception and prior knowledge, constructing a subjective reality.

The McGurk Effect

• The McGurk Effect demonstrates the integration of auditory and visual information in speech perception, where visual cues can alter auditory perception.

• Vision can dominate audition, illustrating the multisensory integration in the brain.

• The effect varies among individuals and is reduced in dyslexia and autism, suggesting differences in sensory integration.

Auditory Cortex

• Located in the Temporal Lobe (Brodmann areas 41 and 42), responsible for processing auditory information.

• Posterior Superior Temporal Gyrus: Involved in integrating audio and visual information in speech processing; crucial for language comprehension.

Frontal Cortex

• Function: Selecting and planning an appropriate response ("What to do about it?"), involving higher-order cognitive functions and motor control.

Prefrontal Cortex

• Rostral to the primary motor cortex, the prefrontal cortex is very large in humans and develops late (20-30 years old), playing a key role in executive functions.

• Dorsal: Thoughts and attention, including working memory and cognitive flexibility.

• Ventral: Emotion and social behavior, influencing decision-making and emotional regulation.

Functions of the Prefrontal Cortex

• Restraint: Judgement, foresight, inhibiting inappropriate actions, and concentration.

• Initiative: Drive, creativity, curiosity, personality, and flexibility.

• Order: Planning, abstract reasoning, working memory, and attention.

Frontal Cortex Damage Symptoms

• Difficulty planning sequences to complete tasks, indicating impaired executive function.

• Loss of spontaneous interactions, reflecting changes in social behavior.

• Loss of flexibility in thought, resulting in rigid and inflexible thinking patterns.

• Perseveration: Persistence of a single thought or action, showing impaired cognitive control.

• Inability to focus on the task in hand, suggesting deficits in attention and concentration.

• Emotional lability, characterized by rapid and unpredictable mood changes.

• Abulia: Passivity, apathy, and a lack of motivation.

• Socially inappropriate behavior, indicating impaired social cognition.

• Personality change, reflecting alterations in character and behavior.

• Difficulty with problem-solving, showing deficits in executive function.

• Expressive aphasia, affecting the ability to produce speech.

• Hemiplegia, causing paralysis on one side of the body.

Executive Function

• Executive function resides in the prefrontal cortex and involves:

  • Long-term planning, setting goals, and strategizing.

  • Withholding impulsive behavior, showing self-control and regulation.

  • ‘Cognitive control,’ enabling flexible and goal-directed behavior.

• Important in pathologies like addiction, personality disorders, and dementia, and in everyday behaviors, influencing decision-making and adaptive behavior.

White Matter Tracts

• Connect the association cortices and different parts of the brain, facilitating communication between brain regions.

• Composed of myelinated neurons, which enhance the speed and efficiency of neural transmission.

Properties of White Matter Tracts

• Not visible by physical exam, CT, or static MRI; require specialized imaging techniques for visualization.

• Use Diffusion Tensor Imaging to map the direction and integrity of white matter tracts.

• Association fibres: Connect cortical areas in the same hemisphere, supporting intrahemispheric communication.

• Commissural fibres: Connect across hemispheres, enabling interhemispheric communication.

• Projection fibres: Connect cortex to other brain regions, such as the spinal cord and thalamus.

• Fasciculus means ‘bundle,’ referring to a collection of nerve fibers.

Examples of White Matter Tracts

• Superior Longitudinal Fasciculus: An Association tract connecting frontal, parietal, and temporal lobes; important for language and attention.

• Corpus Callosum: A Commissural tract that connects the hemispheres, allowing for the transfer of information between them.

• Corticospinal (motor) and Corona radiata: Projection tracts that carry motor and sensory information, respectively.

Language

• Language involves cortical areas working together, including Broca's area, Wernicke's area, and the arcuate fasciculus.

Speech Difficulties

• Dysarthria: Difficulty moving the muscles of the face and tongue that mediate speaking, affecting articulation and speech clarity.

• Aphasia: Difficulty in naming objects and impaired repetition of words; difficulty with language production or comprehension.

Wernicke's Area

• Located in the Temporal Cortex (Posterior Superior Temporal Gyrus, Brodmann Area 22), responsible for understanding language.

Wernicke's Aphasia

• Unable to understand language, resulting in impaired comprehension.

• Fluent speech, but makes no sense, characterized by nonsensical content.

  • Little repetition, showing reduced ability to repeat spoken words.

  • Adequate syntax and grammar, but the content is meaningless.

  • Contrived or inappropriate speech, indicating impaired language processing.

• Damage to Wernicke’s area is often a result of a stroke affecting branches of the Middle Cerebral Artery, disrupting blood supply to the region.

• Also called fluent, sensory, or receptive aphasia, reflecting the nature of the language deficit.

Broca's Area

• Located in the Inferior Frontal Gyrus (Brodmann Areas 44 and 45), responsible for creating language.

Broca's Aphasia

• Few problems understanding language, assuming Wernicke's Area is intact, indicating preserved comprehension.

• Difficulty constructing their own speech, resulting in impaired language production.

  • Halting speech – makes sense?, characterized by effortful and fragmented speech.

  • Repetitive, showing perseveration of words or phrases.

  • Disordered syntax and grammar, affecting sentence structure.

  • Disordered structure of individual words, leading to errors in word formation.

• Also called non-fluent, motor, expressive, or production aphasia, reflecting the nature of the language deficit.

• Damage to Broca’s area is often a result of a stroke affecting different branches of the Middle Cerebral Artery, disrupting blood supply to the region.

Broca vs Wernicke Aphasia

• Broca's Aphasia (Frontal):

  • Understand language, with relatively preserved comprehension.

  • Cannot construct their own, resulting in impaired language production.

  • Halting speech – makes sense?, characterized by effortful and fragmented speech.

  • Repetitive, showing perseveration of words or phrases.

  • Disordered syntax, grammar, and structure of individual words, affecting sentence structure and word formation.

• Wernicke's Aphasia (Temporal):

  • Unable to understand language, resulting in impaired comprehension.

  • Fluent speech, but makes no sense, characterized by nonsensical content.

  • Little repetition, showing reduced ability to repeat spoken words.

  • Adequate syntax and grammar, but the content is meaningless.

  • Contrived or inappropriate speech, indicating impaired language processing.

General Points About Aphasias

• Recognition of ‘conversation cues’ seems OK, indicating some preserved social communication skills.

• Affects other forms of language, including reading, writing, and sign language, showing a global impact on language abilities.

• Many other forms of aphasia exist, reflecting the complexity of language processing in the brain.

Arcuate Fasciculus

• Connects Broca's and Wernicke's areas, enabling communication between language production and comprehension regions.

• Comprised of Association Fibres, facilitating the flow of information between different cortical areas within the same hemisphere.

Summary

• Association cortices process sensory and learned information, integrating inputs from different modalities.

• Posterior Parietal Cortex: Where is it? - Spatial awareness