Exam 4

Semantic information

meaning associated with words.

Syntax

rules for how words are combined to form sentences that people understand

Phonology

the structure of the sounds of the words in a language

Orthography

the written system of language

Mental lexicon

the mental store of information about words, including semantic information, syntactic information, and word forms (how letters and sounds are combined to form words).

4 facts about the mental lexicon

1. Does not have fixed contents—words can be forgotten and new words can be learned.

2. Normal adults store about 55,000 words in their mental lexicon.

3. More frequently used words are accessed more quickly.

4. Organized in information specific networks

Semantic Network Model (Collins & Loftus)

how concepts are represented

• Words are represented by “nodes”, and semantically related nodes are connected with each other.

• Strength and length of the connections reflects the semantic relations: the closer two words are related, the stronger and shorter their connection is.

• When one node is activated, activation spreads to the associated nodes, as well; the shorter the connection, the more activation an associated node will receive.

Evidence for the existence of mental lexicon: concepts are organized in semantically meaningful networks

Language Production

the ability to use words, phrases, and sentences to convey information

Language Comprehension

the ability to understand the messages conveyed by words, phrases, and sentences.

Neural substrates of speech perception

• Left perisylvian language network

• Superior temporal gyrus (STG)

Superior temporal gyrus (STG)

• Lesions cause pure word deafness

• Activation is modulated by whether the incoming auditory signal is speech or nonspeech sounds.

• Acoustic sensitivity decreases moving anteriorly and posteriorly away from the primary auditory cortex.

• Speech sensitivity increases moving anteriorly and posteriorly away from the area immediately surrounding the primary auditory cortex.

pure word deafness

inability to recognize speech sounds, although they can recognize non-speech sounds.

• Due to lesions in STG

ERPs important in language processing

• N400

• P600

P600

syntactic processing; higher when there is a violation of syntax.

N400

• semantic processing; higher when there is a semantic violation

• data that conveys meaningful content rather than just raw symbols

Broca’s aphasia

problems related to producing and understanding syntactic relationships

• Lesions to (but not limited to) the left inferior frontal gyrus (Broca’s area), typically also involve surrounding white matter and subcortical connections.

Issues due to lesions to (but not limited to) the left inferior frontal gyrus

• Broca’s aphasia

  • Expressive aphasia

  • Telegraphic speech

  • Agrammatism

expressive aphasia

impairment is mainly in expressing language using writing and sign languages.

Telegraphic speech

use mainly content words (nouns, pronouns, etc) and lack function words (prepositions, etc), speak in short, simple phrases, many pauses and not fluent

Agrammatism

deficits in processing grammatical aspects of language.

• Ex: “The boy was kicked by the girl" vs. "The boy kicked the girl." The first sentence has a more complicated grammar, confusing patients with Broca's aphasia about who kicked whom.

Wernicke’s aphasia

disturbance in comprehension in the presence of fluent (but meaningless) speech.

• Lesions to the posterior third of the left superior temporal gyrus

Issues due to lesions to the posterior third of the left superior temporal gyrus

• Wernicke’s aphasia

  • receptive aphasia

  • Word salad: a confused or unintelligible mixture of seemingly random words and phrases

  • Neologisms: invent new words themselves

  • Semantic paraphasias: generate words related to the meaning of the intended word (saying “cow” while wanting to say “horse”).

Conduction aphasia

problems spontaneously producing and repeating speech.

• Damage to the arcuate fasciculus, a bundle of axons that links Broca’s and Wernicke’s areas.

• Have problems in moving linguistic information rapidly from input to output stages.

• Can understand words and hear their own speech errors.

Global aphasia

inability to comprehend or produce speech.

• Produced by extensive lesions in the left perisylvian area.

• Symptoms may include the disabilities of the other three types of aphasia.

Dyslexia

difficulty in reading, not due to a sensory or intellectual impairment.

• Due to problems with the language network: less activity in Wernicke’s area.

• Compensatory activity in the left anterior language areas and the right hemisphere.

Cognitive control

• Mental abilities that involve planning, controlling, and regulating the flow of information processing

• Essential for successful completion of goal-directed behavior and decision making

PFC

the CEO, conductor, air-traffic controller metaphors

Anatomy of Cognitive Control

• Lateral PFC

• Ventromedial PFC (vmPFC) /orbitofrontal cortex (OFC)

• Medial frontal cortex /Anterior cingulate cortex (ACC)

Lateral PFC

selective attention, short-term memory, planning, action selection, response inhibition (recall topics covered in previous modules, such as attention & memory)

Ventromedial PFC (vmPFC) /orbitofrontal cortex (OFC)

emotion and reward processing, decision making

Medial frontal cortex /Anterior cingulate cortex (ACC)

error detection, resolving conflict, rational cognitive functions.

Successful goal directed behavior involves:

• The initiation of behavior

• The creation and maintenance of a goal or plan

• Sequencing

• Maintaining relevant information in working memory

• Switching or shifting

• Inhibition

• Self-monitoring and evaluating

Planning

• Complex goals need to be translated into plans and strategies for action to be taken.

• To achieve a goal, planning needs to happen at multiple levels.

• Dorsolateral PFC is involved in goal planning.

  • PFC damage is associated with Psychological Inertia, characterized by difficulties in starting an action or behavior, and, once engaged in action, difficulties stopping it

  • (remember patient W.R., who consulted a neurologist because he “lost his ego.”)

Sequencing

• To choose the order in which actions are taken to best achieve the goal.

• Demonstrated by the Tower of London task: patients with PFC damage take more moves to obtain the goal → do the task by trial and error, and not planning

• Dorsolateral PFC is also involved

Goal maintenance

• To maintain the current goal, and to resist distractions/interference.

• Involves selecting task relevant information and/or filtering out the task-irrelevant information.

• Involves PFC. Patient with PFC damage wander off task.

  • PFC as a dynamic filtering mechanism: maintains relevant information in working memory.

  • Demonstrated by the Stroop task: we might selectively enhance info (color) or inhibit the irrelevant info (word)

Switching

• Ability to shift from one subgoal to another in an appropriate manner to achieve the overall goal; also involved in multi-tasking, when attention is quickly shifting among multiple tasks.

• Wisconsin Card Sorting Task: subjects sort cards according to arbitrary rules, and rules change frequently.

  • Frontal lobe patients show perseveration—difficulty in adjusting responses when the rules have changed, and the original responses are no longer appropriate.

  • Perseveration implies a lack of cognitive flexibility.

• Networks composed of regions in the PFC and parietal cortex work together

Inhibition

• Go/No-Go task. Brain activity during successful 'no-go' trials is considered as an index of response inhibition, and the proportion of errors on 'no-go' trials is considered a behavioral marker of impulsivity.

• PFC regions are involved in inhibiting responses.

  • Ex: Food Go/No-Go task paradigm. Successful weight losers had greater activation in the dorsolateral PFC when viewing high-energy food, whereas overweight participants had greater activation in ventral striatum and anterior cingulate.

Goal Monitoring

• Monitoring is necessary to ensure the success of goal directed behavior. Anterior cingulate cortex (ACC) is critical for monitoring.

• Two theories

  • Error detection hypothesis

  • Response conflict hypothesis

Error detection hypothesis

ACC is involved in detecting errors, which serves to increase cognitive control.

• The ERP component, Error-related potential (ERN), is generated by the ACC; it shows up when people make an incorrect response.

• ERN amplitude is reduced in frontal lobe patients, but increased in patients with obsessive-compulsive disorder.

Response conflict hypothesis

ACC is involved in evaluating response conflict (encompassing the higher-level attention and error detection functions).

• Supporting evidence: Stroop task. ACC activity is high for incongruent trials, even though people usually do not make mistakes on these trials

• ACC activity is modulated by monitoring demands.

Self-referential effect

• enhanced memory for information processed in relation to the self

• Theories:

  • Depth of processing hypothesis

  • Alternative hypothesis

• Kelley et al. studies: Medial prefrontal cortex (MPFC) differentially activated when judging personality adjectives in relation to the self → supported the uniqueness hypothesis.

• People use different sources of information when making self-descriptive judgments: we rely on ‘summaries’/overall impressions of our personality instead of specific episodes → supported the uniqueness hypothesis.

  • Retrograde amnesiacs maintain knowledge of their own personality.

Depth of processing hypothesis

better memory because of deeper processing (more attention, more associations).

Alternative hypothesis

the self is a special cognitive structure with a unique organization, and its processing is just different from the processing of other information. This would predict that self referential processing is supported by distinct neural systems.

Self-reference as our “Default Mode”

• Resting-state fMRI reveals a “default mode network” (MPFC and other regions) that is active when we do not engage in tasks, and is deactivated during externally-driven/goal-directed tasks.

  • Also involved in tasks that require viewing from an alternative perspective (across time and/or space): autobiographical memory, envisioning future, moral dilemma, theory of mind.

Positive self-perception

• People generally have positive self-views. But people with depression have unrealistically negative self-regard.

• Higher-order prefrontal cortex regions (ACC, OFC) may work together to permit a focus on positive aspects of self without deviating too far from reality.

• Beer et al study: Patients with OFC damage tend to have unrealistically positive selfperceptions.

  • When engaged in a social conversation, they exhibit inappropriate behavior but are embarrassed afterwards when watching themselves do so → they have the knowledge of social norms, but fail to bring online this knowledge to modulate behavior. → lack of insight into their behavior at the moment. → OFC is important for spontaneous, accurate self-perception.

Theory of mind (mentalizing)

the ability to make inferences about the mental states of other people (mental states may not be obvious from other’s outward behavior).

• False belief tests (e.g., Sallie-Ann task): children typically pass false belief tests around 4-5 years old; children with autism do not. Autistic children may fail false belief tasks even if they previously held a false belief themselves (ex: Smarties task).

Neural mechanisms of theory of mind

• Temporal parietal junction (TPJ)

• Medial PFC:

ToM: Temporal parietal junction (TPJ)

specialized for reasoning about the mental states of others. Important for redirecting attention in both social and nonsocial situations. Lesions in this region can lead to impairments on theory-of-mind tasks

ToM: Medial PFC

involved more broadly in reasoning about other people (than thinking about other entities). Supports reasoning about social tasks. Lesions here don’t necessarily disrupt performance on ToM tasks.

• Saxe et al. study: activity in the right TPJ when comparing false belief tasks (that require mentalizing) with false photographs tasks (that do not require mentalizing, but involve a conflict with reality).

Mirror neurons system

includes the premotor cortex, parts of the superior temporal sulcus, and the intraparietal cortex

• active when performing a particular movement or when observing another perform the same action

Mirror neurons system VS Mentalizing system:

• Both engage TPJ areas.

• The mirror system relies more on the lateral motor cortex, which is involved in observing or performing specific actions.

• The theory of mind system relies more on the medial PFC, which is involved in perceiving self/other’s mental states.

ASD is a developmental disorder identified by DSM 5 as being associated with

1. deficits in social communication/interaction

2. restricted and repetitive behaviors.

Explanations for ASD

• Mind blindness theory: fundamental deficits in theory of mind.

• Broken mirror theory: fundamental deficits in the mirror neurons system.

  • People with autism fail to exhibit automatic mimicry, which may be due to their inability to represent coherent action chains that allow motor intentions to be understood.

Neuroplasticity

the brain's malleability and ability to change.

T or F:

• Newborn brain: about 450 grams, adult size brain: about 1,400 grams.

• Most neurons are formed before birth.

• The increasing brain volume after birth is mainly caused by the growth of synapses, by increasing in the size of dendritic arborizations, extensions of the axons, by the proliferation of the glial cells, and the myelination of nerve fibers.

true

Synaptogenesis

• The formation of new synapses in the CNS

• Has a rise and fall/ inverted U pattern: it peaks soon after birth, with different cortical regions reaching the peak at different times (primary sensory and motor areas first, PFC last), and then it falls (see figure above).

synapse elimination/pruning

interconnections between neurons that are redundant, unused, or not functional are eliminated.

Myelination

• the increase in glial cells that provide the fatty layer that surrounds the axons, and increases the speed of information processing.

• Early in life, the most myelinated brain regions are those that support basic functions, such as the spinal cord and the medulla.

• The prefrontal cortex is one of the latest areas to achieve adult levels of myelination (see figure above).

What does early maturation of the limbic regions, late maturation of the prefrontal cortex cause?

Increased reward-based behavior, coupled with less cognitive control.

Sensitive periods

a time in life when plasticity in greater.

Early studies in rats:

• Dr. Marion Diamond: enriched environments produce anatomical changes in the rats' cortex => more extensive arborizations, while deprived environments => dendrites shrinking to the point of total disappearance.

Structural and functional brain changes (pos or neg) may be caused by:

• Damage to the brain following traumatic brain injury or certain types of disease (e.g., Alzheimer's).

• Activities: exercise/ training, meditation, learning, etc.

Physical Exercise

• Affects the structure and function of the hippocampus and the prefrontal cortex.

• Increases the production of neurotransmitters, including serotonin and nor-adrenaline, stimulating the blood flow, and stimulating adult neurogenesis.

Meditation Training

• Associated with enlarged volumes of the hippocampus, cerebellum and prefrontal cortex areas.

Three main subdivisions of the prefrontal cortex are the:

1. Lateral prefrontal cortex

2. Frontal pole

3. Medial frontal cortex

One of the basic steps involved in reaching a goal is determining what steps to take to attain the goal, and the order in which these steps must be taken.

Sequencing

What part of the brain is associated with the generation of an "error potential"?

Anterior cingulate cortex