Executive Function and Language

Overview of Higher Cognitive Functions

Executive Function Objectives

  • Identify executive functions:

    • Functions considered to be part of executive function include:

    • Action selection

    • Impulse control

    • Risk assessment

    • Working memory

    • Attention

    • Planning

    • Decision-making

    • Emotional control

    • Long-term memory retrieval

  • Neuronal correlates:

    • Identify the neuronal correlate of working memory in the dorsolateral prefrontal cortex (dlPFC) of primates.

  • Executive functions in decision-making:

    • Identify prefrontal cortical regions associated with:

    • Valuation

    • Risk assessment

    • Decision-making (action selection)

  • Neuromodulator influence:

    • Describe how neuromodulators affect neuronal excitability and optimize activation of neurons.

The Prefrontal Cortex (PFC) and Executive Function

  • What is “executive function”? Critical areas include:

    • Action selection

    • Impulse control

    • Risk assessment

    • Working memory

    • Attention

    • Planning

    • Decision-making

    • Emotional control

    • Long-term memory retrieval

integrating everything we learn to choose the appropriate actions for the given situation. How we decide what to do (or not to do) and when to do it. 

  • The prefrontal cortex is a collection of highly interconnected areas that interact functionally.

    • Receives input from several brain regions, including:

    • Memory areas

    • Sensory areas

    • Internal state signals

    • Motor feedback

  • The PFC outputs to motor areas, controlling behavior and also feeding back to input regions. It mainly influences behavior via:

    • Striatal pathways

    • Thalamocortical loops

Examples of Executive Function

  • Key points include:

    • Maintenance of recent experiences and future action plans in the absence of sensory input is described by working memory.

    • Evaluation of risk and reward contributes to action selection and impulse control.

    • Development of rules and adapting behavior to changing scenarios exemplifies cognitive flexibility and attentional set-shifting.

Decision Making and Action Selection

  • Reward vs. Risk: Making effective decisions requires evaluating consequences, both risks and benefits, and considering the timing of outcomes.

  • Neuroeconomics (neuroscience of decision making) acts as:

    • Valuation System: Rankings of choices utilize the ventromedial prefrontal cortex (vmPFC) and anterior cingulate, along with the dopamine reward system.

    • Choice System: Involves several prefrontal areas (dorsolateral prefrontal cortex, dorsal anterior cingulate cortex) and parietal regions to assess alternatives and make decisions.

Delay Discounting and Reward Choices in Rats

  • The concept of value choice in terms of rewards:

    • Small vs. large rewards are assessed against associated costs, such as time delays.

  • Rats can effectively identify optimal choices to maximize rewards within given timelines.

Impacts of Prefrontal Cortex Dysfunction

  • Damage or dysfunction in the PFC results in impulsive behaviors, indicating a preference for immediate rewards without regard for cost.

  • Specific PFC areas involved:

    • Ventromedial prefrontal cortex (vmPFC) and orbital prefrontal cortex (OFC) assess value and risk associated with different outcomes.

    • Dorsolateral prefrontal cortex (dlPFC) is crucial in decisions based on these evaluations. Weighs the risk and reward to make decision.

  • Correlation between strengths of connections between these areas indicates lower impulsivity and a better ability to delay gratification.

Feedback Mechanisms in Decision Making

  • Future decisions are influenced by outcomes from past choices:

    • Activation of the amygdala and orbitofrontal cortex corresponds with costly decisions, indicating:

    • Diminished reward

    • Aversion to loss.

  • Attention Deficit/Hyperactivity Disorder (ADHD) links:

    • Aberrant functions in the prefrontal cortex and striatum increase impulsivity and reduce behavioral support from delayed reinforcement.

    • Children with ADHD show delayed matured PFC but demonstrate high reinforcement value leading to focused attention capabilities.

    • * Remember the role of the mesolimbic dopamine system in reinforcement learning! 

Catecholamines and ADHD Treatment

working memory and attention require optimal levels of catecholamines

  • Treatments for ADHD often target catecholamine systems:

    • Stimulants blocking reuptake affect neurotransmitter levels (e.g., norepinephrine, dopamine).

  • The Val-val genetic variant indicates increased levels of COMT enzyme leading to diminished catecholamines,

  • whereas the Met-met variant shows reduced COMT levels with an increase in catecholamines.

  • Catechol-O-methyltransferase (COMT) breaks down catecholamines post-release influencing working memory dynamics.

Neuromodulation Concept

Neuromodulators can bring the membrane potential closer (increase exc.) or further away (decrease exc.) from the threshold of excitation - thereby “modulating” cellular excitability. 

  • Graphical Data:: shows the biphasic dose–response relationships for norepinephrine-modulation in rat sensory cortical neurons:

    • Demonstrated through various administered levels of NE (1-20 nA), influencing glutamate-evoked responses maximally via intermediate doses.

    • Too little NE results in insufficient receptor activation while excessive NE activates low-affinity receptors leading to diminished responses.

Key Functions of the Prefrontal Cortex in Executive Function

How do we decide what to do (or not to do) and when to do it?

  • Functions include:

    • Recalling similar past situations and their outcomes.

    • Focusing on relevant tasks while ignoring distractions.

    • Maintaining pertinent information while disregarding distractors.

    • Evaluating emotional and motivational values, including risks associated with potential actions.

    • Planning, choosing, and executing appropriate behaviors.

Language Learning Objectives

  • Core Objectives:

    • Describe language development stages.

    • Identify brain areas mediating language components (grammar, semantics, prosody).

    • Discuss specific language deficits and brain areas implicated in Broca’s and Wernicke’s aphasias as per connectionist models.

  • Required Reading:

    • Chapter 19 (Sections 19.1, 19.3, 19.4, 19.5.1) and optional sections on Reading and Writing.

Language Definition and Components

  • Language includes:

  • what is language? comprehension and speech

    • Comprehension:

    • Listening and reading comprehension involves recognizing words, understanding word meaning, and capturing emotional content.

    • Speech Production (talking/writing):

    • Involves fine motor commands for coordination of mouth parts (facial, jaw, tongue, lips, vocal cords) and requires sensory feedback (hearing your voice).

Language Rules

  • Components: Grammar and Syntax (organizational rules of language):

    • Semantics: (meaning associated with words).

    • Example distinctions between grammar and semantic impairments:

    • Grammar impaired but semantics intact: “Boy…ball…hit.”

    • Grammar intact but semantics impaired: “The raven was hijacked in Denmark.”

Language Learning in Young Birds vs. Human Infants

* Critical period of language acquisition 

  • Birdsong as a Model:

    • Language acquisition parallels observed in bird song learning:

    • Stage 1: Young males store song patterns learned from fathers. (sensory feedback)

    • Stage 2: They trial and error their song, starting from pogosticking/babbling stage. (instrumental learning)

    • Stage 3: Finally, crystallization into a permanent form takes place. (end of “critical period”)

    • Babbling = trial and error learning

    • plasticity in language and motor aress of the brain

  • Language learning is social

    • birds and humans require a live tutor in order to learn language 

  • First Year of Language Development in Humans and Birds:

    • Sign language babbling shows parallel trials and developments.

Language Processing in the Brain

  • Primary cortical areas for language consist of regions that facilitate comprehension and production:

    • Specialized areas connect sensory and motor responses involved in articulating speech.

  • Speech produciton- sensory activation to motor production

    • wernicke’s area, broca’s area

Lateralization of Language Function

  • Left Hemisphere Functions:

    • Primary for language production and comprehension.

  • Right Hemisphere Functions:

    • Associated with prosody (melody, tone of voice, stress on words and syllables), emotional aspects of speech, humor, metaphor comprehension. right side of language system is activated for metaphors. 

Aphasia and its Types

KNOW FOR EXAM : Broca’s  and Wernicke’s aphasia 

know the brain areas, language system effected 

  • Types of Aphasia:

    • Broca’s Aphasia

    • Characterized by halting speech, repetitive errors, disordered grammar, but semantically adequate.

    • Wernicke’s Aphasia

    • Notable for fluent yet nonsensical speech, impaired comprehension.

  • Broca’s Aphasia Characteristics:

    • Phonetic production coupled with comprehension difficulties. (E.g., agrammaticism, anomia, articulation deficits)

  • Wernicke’s Aphasia Characteristics:

    • Loss of comprehensive capabilities and coherent word retrieval; often leads to a nonsensical output.

  • Connectionist Model of Aphasia exemplifies key issues in producing or comprehending language, detailing varying types:

    • Broca’s, Wernicke’s, pure word deafness, transcortical sensory aphasia, conduction aphasia, and anomic aphasia.