HIGHER CORTICAL FUNCTIONS

Osama RagabAss.Lec of Neurology

2014

Which is true

I think; therefore I am.

I have brain activation, therefore

I am.

introduction

the higher cortical functions makes up the conscious mind.

Memory , language, calculations, spatial topography and reasoning, executive function, music, and creativity all represent functions higher functions.

The term intellect designates the totality of the mental operations that comprise human thought.

Cerebral Cortex

Cerebral Cortex

The cortical mantle of the human brain contains more than 14 billion neurons.

within the cortical mantle, the association cortices, cortical zones that do not carry out primary motor or sensory represent 75% of the cerebral cortex.

Each of the primary cortices receives signals in only one modality (vision, hearing, or sensation) and has connections only to association cortex also dedicated to this modality(unimodal association cortex) .

Unimodal association cortices communicate with each other via more complex connections to the heteromodal association cortex.

Cerebral Cortex

heteromodal association cortex The posterior heteromodal association cortex

involves the posterior inferior parietal lobe, especially the angular gyrus. it perceive an analogy association (picture of boat &word boat).

the lateral prefrontal region ,This region is thought to be involved with attention or “working memory” and with sequential processes such as storage of temporally ordered stimuli and the planning of motor activities(excutive functions).

supramodal cortex

The Orbitofrontal cortex is known as the supramodal cortex because it relates the functions of the heteromodal cortex regarding attention and sequencing of responses with interoceptive inputs from the internal milieu of the body.

The orbitofrontal area has close connections with the limbic system and autonomic, visceral, and emotional processes.

Cerebral cortex architecture

Cerebral cortex architecture

Cerebral cortex architecture

the cerebral cortex is subdivided into limbic cortex, paralimbic cortex,and neocortex

The limbic cortex is the most primitive cortical area and includes the amygdala and hippocampal formation.

The paralimbic cortex includes the parahippocampal cortex and cingulate cortex of the medial wall of the hemisphere and portions of the frontal and temporal lobes and the insula.

The frontal lobe

The parietal lobe

The temporal lobe

The occipital lobe

Neocortical Networks

Several neocortical networks involve interactions among different primary, unimodal, and heteromodal association areas. These networks are important in the following functions:

1-sensory processing and object recognition. 2- directed attention. 3- motor programming and execution. 4- language . 5. control of behavior. 6. Memory.

sensory processing and object

recognition.

Visual System

the primary visual cortex area 17,calcarine or striate cortex.

Further processing involves unimodal visual association areas, namely, areas 18 and 19 .

The dorsal stream of visual processing involves areas in the middle temporal and middle superior temporal lobe and terminates in the posterior parietal analyzing the location and movement of an object.

In the ventral stream, the color and form of an object are analyzed in a sequentially hierarchical fashion by neurons located in the fusiform and lingual gyri.

Auditory System

The auditory cortex is divided into a core,a belt, and a parabelt that participate in the sequential processing of auditory information.

The core is the primary auditory area and contains neurons that respond to pure tones of specific frequencies and respond primarily to stimulation of both ears.

The belt contains neurons that respond to complex sounds.

The left superior temporal gyrus is critical for the acoustic processing and extraction of the meaning of spoken language.

The temporal lobe

Object Recognition and Semantic Knowledge

Object recognition is the first necessary step for naming, using, and reacting emotionally to an object.

information about different object stored particularly in the left hemisphere.

The ability of modality-specific visual, somatosensory, or auditory information to activate the relevant multimodal associations that lead to face or object recognition depends on a heteromodal network located in the anterior middle temporal gyrus and temporal pole.

Agnosia

Agnosias are disorders of recognition. “normal percept stripped of its

meaning.” Sigmund Freud originally introduced

the term agnosia in 1891 to denote disturbances in the ability to recognize and name objects, usually in one sensory modality in the presence of intact primary sensation.

Criteria for the diagnosis of agnosia include:

(1) failure to recognize an object. (2) normal perception of the object,

excluding an elementary sensory disorder.

(3) ability to name the object once it is recognized, excluding anomia as the principal deficit.

(4) absence of a generalized dementia.

Agnosia

Visual Object Agnosia

The patient fails to recognize objects by sight, with preserved ability to recognize them through touch or hearing in the absence of impaired primary visual perception or dementia.

Two subtypes of visual object agnosia: apperceptive visual object agnosia, referring to

the synthesis of elementary perceptual elements into a unified image is lost.

associative visual object agnosia, in which the meaning of a perceived stimulus is appreciated by recall of previous visual experiences is lost.

Apperceptive Visual Agnosia

Patients with apperceptive visual agnosia can pick out features of an object correctly (e.g., lines, angles, colors, movement), but they fail to appreciate the whole object.

the medial occipital cortex related to appreciation of color and texture, whereas the lateral occipital cortex is more involved with shape perception.

Apperceptive Visual Agnosia

Associative Visual Agnosia

inability to connect the visual percept with its related semantic information stored in memory, such as, its name, use, and description.

Most but not all cases of associative visual agnosia have involved the fusiform or occipitotemporal gyri bilaterally.

Optic Aphasia The syndrome of optic aphasia, or optic anomia, is

intermediate between agnosias and aphasias. The patient with optic aphasia cannot name

objects presented visually but can demonstrate recognition of the objects by pantomiming or describing their use.

The preserved recognition of the objects distinguishes optic aphasia from associative visual agnosia.

Like visual agnosics, patients with optic aphasia can name objects presented in the auditory or tactile modalities, distinguishing them from anomic aphasics.

In optic aphasia, information about the object is not available to the language cortex for naming.

Patients with optic aphasia frequently manifest associated deficits of alexia without agraphia and color agnosia, suggesting a left occipital lesion.

Optic Aphasia

Prosopagnosia

Prosopagnosia refers to the inability to recognize faces.

they learn to compensate by identifying a person by voice, mannerisms, gait patterns, and apparel.

the inferior occipital lobe and the middle fusiform gyrus are involved in aspects of face perception.

Anton syndrome

Some patients with cortical blindness are unaware that they cannot see, and some even confabulate visual descriptions or blame their poor vision on dim lighting or not having their glasses (Anton syndrome).

Patients with Anton syndrome may describe objects they “see” in the room around them but walk immediately into the wall.

The thinking and speaking areas of the brain are not consciously aware of the lack of input from visual centers.

Balint Syndrome

(1) psychic paralysis of gaze, also called ocular motor apraxia, or difficulty directing the eyes away from central fixation.

(2) optic ataxia, or incoordination of extremity movement under visual control (with normal coordination under proprioceptive control.

(3) impaired visual attention. These deficits result in the perception of only small

details of a visual scene, with loss of the ability to scan and perceive the “big picture.” Patients with Balint syndrome literally cannot see the forest for the trees.

loss of ability to perceive more than one item at a time.

these patients can often read “letter-by-letter,” or one letter at a time, but they cannot recognize a word at a glance.

Many such patients have left occipital lesions and associated pure alexia without agraphia.

Simultanagnosia

Auditory agnosias can be divided into

(1) pure word deafness. (2) pure auditory nonverbal

agnosia. (3) phonagnosia, or inability to

identify persons by their voices . (4) pure amusia. Patients may have one or a mixture

of these deficits.

Auditory Agnosias

Cortical Deafness

Profound hearing deficits are seen in patients with acquired bilateral lesions of the primary auditory cortex (Heschl gyrus, Brodmann areas 41 and 42) or of the auditory radiations projecting to the Heschl gyri.

Pure Word Deafness

The syndrome of pure word deafness involves an inability to comprehend spoken words, with preserved ability to hear and recognize nonverbal sounds.

Pure word deafness has traditionally been explained as a disconnection of both primary auditory cortices from the left hemisphere Wernicke area.

Auditory Nonverbal Agnosia

Auditory nonverbal agnosia refers to patients who have lost the ability to identify meaningful nonverbal sounds but have preserved pure tone hearing and language comprehension. These cases also tend to have bilateral temporal lobe lesions.

Phonagnosia

it is a failure to recognize familiar people by their voices.

usually reflecting unilateral or bilateral temporal damage, but failure to recognize a familiar voice may involve a right parietal locus corresponding to the specific area for recognition of faces.

Amusia

recognition of melodies and musical tones is a right temporal function, whereas analysis of pitch, rhythm, and tempo involves the left temporal lobe.

tactile agnosia

Lesions of the postcentral gyrus that interrrupt the connections between the primary and unimodal somatosensory association areas in the parietal lobe cause tactile agnosia , or astereognosia, inability to recognize letters or numbers written on the palm of the hand (agraphesthesia), inability to localize touch (atopognosia), and loss of ability to discriminate weights (abarognosia) on the contralateral side.

semantic dementia

Lesions in the anterior middle temporal or temporopolar cortex, particularly on the left side,deprive the person of the ability to associate multimodal information needed to recognize objects via different modalities.

These patients become progressively unfamiliar with objects, leading to progressive loss of knowledge of the world.T

Spatial Attention

Spatial Attention

Neurons of the intraparietal sulcus integrate visual, somatosensory, and auditory information to encode a representation of space.

This is forwarded to the premotor cortex and frontal eye fields to initiate reaching and grasping for objects and directing gaze toward contralateral space.

Damage to the parietotemporal region, typically in the right hemisphere, produces contralateral spatial neglect .

Language

Language

Language is a complex system of communicating symbols and rules for their use.

Aphasia is defined as a disorder of language acquired secondary to brain damage.

aphasia is distinguished from congenital or developmental language disorders, called dysphasias. (in British usage the term dysphasia applies to partial or incomplete aphasia.)

Apraxia of speech is a syndrome of misarticulation of phonemes, especially consonant sounds. Unlike dysarthria, in which certain phonemes are consistently distorted.

Clinically, speech-apraxic patients produce inconsistent articulatory errors, usually worse on the initial phonemes of a word and with polysyllabic utterances.

Language

Phonemes are the smallest meaning-carrying sounds. morphology is the use of appropriate word endings

and connector words for tenses, possessives. semantics refers to word meanings. the lexicon is the internal dictionary. syntax is the grammatical construction of phrases . Pragmatics refers to the proper use of speech and

language in a conversational setting, including pausing while others are speaking, taking turns properly, and responding to questions.

Language

Anomia, or inability to produce a specific name. Anomia is manifested in aphasic speech by word-

finding pauses and circumlocutions, or use of a phrase when a single word would suffice (e.g., “the thing you tell time with” for watch).

Paraphasic errors are divided into literal errors involving substitution of an incorrect sound (e.g., “shoon” for “spoon”) and semantic errors involving substitution of an incorrect word (e.g., “fork” for “spoon”).

A pattern of paraphasic errors and neologisms is called jargon speech.

Language

Relevant Neuroanatomy

Reception spoken language take place in auditory cortex, the Heschl gyrus, in each superior temporal gyrus.

Decoding sounds into linguistic information involves Wernicke area which gives access to a network of cortical associations to assign word meanings.

For both repetition and spontaneous speech, auditory information is transmitted to the Broca area in the posterior inferior frontal gyrus.

Language

The inferior parietal lobule, especially the supramarginal gyrus, also may be involved in phoneme processing and repetition and speech.

Reading requires perception of visual language stimuli by the occipital cortex, followed by processing heteromodal association cortex of the angular gyrus.

Writing involves activation of motor neurons projecting to the arm and hand.

cortical centers involved in cognitive processes project into the primary language cortex, influencing the content of language.

Language

Bedside Language Examination

1.  Spontaneous speech2.  Naming3.  Auditory comprehension4.  Repetition5.  Reading6.  Writing

A speech sample may be elicited by asking the patient to describe the reason for coming to the doctor.

Fluent speech flows rapidly and effortlessly; nonfluent speech is uttered in single words or short phrases, with frequent pauses and hesitations.

Attention should first be paid to such elementary characteristics as initiation difficulty, articulation, phonation or voice volume, rate of speech, prosody or melodic

intonation of speech, and phrase length. Second, the content of speech utterances should be

analyzed in terms of the presence of word-finding pauses, circumlocutions, and errors such as literal and verbal paraphasias and neologisms.

Bedside Language Examination

Naming, the second part of the bedside examination, is tested by asking the patient to name objects, object parts, pictures, colors, or body parts to confrontation. A few items from each category should be tested because anomia can be specific to word classes

Auditory comprehension is tested first by asking the patient to follow a series of commands of one, two, and three steps.

Because apraxia is difficult to exclude it is advisable to test comprehension by tasks that do not require a motor act, such as yes/no questions.

Bedside Language Examination

Broca Aphasia

Aphemia

A rare variant of Broca aphasia is aphemia, a nonfluent syndrome in which the patient initially is mute and then becomes able to speak with phoneme substitutions and pauses.

All other language functions are intact, including writing.

This results from small lesions of the Broca area or its subcortical white matter or of the inferior precentral gyrus.

Wernicke Aphasia

Pure Word Deafness

Pure word deafness is a rare but striking syndrome of isolated loss of auditory comprehension and repetition, without any abnormality of speech, naming, reading, or writing.

Hearing for pure tones and nonverbal noises (e.g., animal cries) is intact.

bilateral lesion isolating the Wernicke area from input from both the Heschl gyri.

Global Aphasia

Conduction Aphasia

striking deficit of repetition. Most patients have relatively normal

spontaneous speech, although some make literal paraphasic errors .

Naming is impaired to varying degrees, but auditory comprehension is preserved.

The lesions of conduction aphasia usually involve either the superior temporal or inferior parietal region.

Anomic Aphasia

Anomic aphasiarefers to aphasic syndromes in which naming, or access to the internal lexicon, is the principal deficit.

Spontaneous speech is normal except for the pauses and circumlocutions produced by the inability to name.

Angular gyrus as the site of lesions producing

anomic aphasia,

Transcortical Aphasias

Repetition is normal. The lesions disrupt connections from other

cortical centers into the language circuit. Mixed transcortical aphasia, with large

watershed infarctions of the left hemisphere or both hemispheres.

Transcortical motor aphasiaoccurs with lesion is watershed between MCA &ACA.

transcortical sensory aphasia, lesion is watershed between MCA &PCA.

Subcortical Aphasias

Left thalamic hemorrhages frequently produce a Wernicke like fluent aphasia with better comprehension than in cortical Wernicke aphasia.

basal ganglia hemorrhages, especially those involving the putamen, the most common site of hypertensive intracerebral hemorrhage. Here the aphasic syndromes are more variable, but most commonly involve global or Broca like aphasia

Pure Alexia without AgraphiaAlexia, acquired inability to read

This ,the patients can write but cannot read their own writing.

On bedside examination, speech, auditory comprehension, and repetition are normal.

Naming may be deficient, especially for colors.

The causative lesion in pure alexia is, with infarction of the medial occipital lobe, often the splenium of the corpus callosum, and often the medial temporal lobe

Pure Alexia without Agraphia

Alexia with Agraphia

acquired illiteracy in which a previously literate patient is rendered unable to read or write.

The oral language modalities of speech, naming, auditory comprehension, and repetition are largely intact.

The lesions typically involve the inferior parietal lobule, especially the angular gyrus.

Agraphia

writing may be affected either in isolation (pure agraphia) or in association with aphasia (aphasic agraphia).

writing can be impaired by motor disorders, apraxia, and visuospatial deficits.

Isolated agraphia has been described with left frontal or parietal lesions

Language in Right Hemisphere Disorders

left-handed patients may have right hemisphere language dominance

Right-handed patients occasionally become aphasic after right hemisphere strokes, a phenomenon called crossed aphasia.

Syndromes of loss of emotional aspects of speech are termed aprosodias.

loss of comprehension of affective language, also called affective agnosia.

right hemisphere–damaged patients understand what is said, but not how it is said.

Memory

Memory

Memory is the recording, retention, and retrieval of knowledge.

It accounts for all knowledge gained from experience—facts that are known, events that are remembered, and skills that are gained and applied.

Types of Memory

Types of memory

Declarative (Explicit) Nondeclarative (Implicit)

Episodic Semantic Procedural ConditioningPriming

Declarative memory is responsible for the learning and remembrance of new events, facts, and materials.

it encompasses both episodic memories (remembrance of personal experiences that took place at a particular place and time) and semantic memories (knowledge of generic information, such as the meaning of a word).

It is the form of memory people use to recollect facts and events consciously and intentionally and is therefore also referred to as explicit memory.

Types of Memory

Nondeclarative memory refers to the many forms of memory that are not retrieved intentionally but reflexively or incidentally.

Implicit forms of memory include perceptual, motor, and cognitivebskill learning(sometimes referred to as procedural memory).

classic and other sorts of conditioning repetition priming, which is the facilitated

processing of a stimulus, such as a word or picture, due to prior exposure to that stimulus.

Types of Memory

 Temporal classification.

Immediate memory refers to the recall of information without delay, either immediately after presentation or after uninterrupted rehearsal.

Immediate memory is characterized by sharply limited capacities for how much and how long information can be remembered.

Working memoryis a multicomponent psychological system that mediates the temporary processing and storage of internal representations that guide and control action. Information is held in working memory only as long as it is useful for solving a problem at hand.

Immediate memory refers to the amount of information a subject can keep in conscious awareness without active memorization. The normal human being can retain seven digits in active memory span.

The second stage of memory, referred to by clinicians as short-term or recent memory, involves the ability to register and recall specific items such as words or events after a delay of minutes or hours.

Long-term memory refers to permanent and large stores of episodic and semantic memories.

 Temporal classification.

Anatomy of Declarative Memory

Anatomy of Declarative Memory

Long-term memories are thought to be stored in the neocortex, the neocortical location reflecting the content of the memory.

the hippocampal formation is important for combining distinct, domain-specific features of an experience.

neocortical damage is thought to result in domain specific memory deficits in which the loss of old memories and the inability to gain new memories reflect the kind of knowledge represented in that neocortical region.

damage to medial temporal lobe, diencephalic, and basal forebrain regions yields widespread, or domain-independent, declarative memory deficits.

The basal forebrain is composed of midline structures, including the septal nuclei, diagonal band of Broca, and substantia innominata. These regions provide the largest input of acetylcholine, the neurotransmitter most directly implicated as critical for declarative memory, to the hippocampus and many neocortical areas.

Anatomy of Declarative Memory

Anatomy of Nondeclarative Memory

Each specific form of nondeclarative memory, however, is closely linked to specific brain structures and regions.

For immediate auditory memory, left and right temporal-parietal cortices, respectively, mediate auditory verbal and nonverbal material.

For immediate visual memory, left and right occipitoparietal cortices, respectively, mediate immediate verbal and nonverbal material.

Working memory linked to the dorsolateral frontal cortex and to basal ganglia and cerebellar areas .

Amnestic Syndrome

The amnestic syndrome refers to profound loss of episodic, recent, or short-term memory.

These patients, most of whom have bilateral hippocampal damage, have normal immediate memory span and largely normal ability to recall remote memories such as their childhood upbringing and education.

Other cognitive or higher cortical functions may be completely intact, which distinguishes these patients from those with dementias .

Transient Amnesia

transient global amnesia, lasting from several to 24 hours.

cognitively intact individual suddenly loses memory for recent events, asks repetitive questions about his or her environment, and sometimes confabulates.

During the episode, the patient has both anterograde and retrograde amnesia, as in the permanent amnestic syndrome.

The syndrome may be related to partial complex seizures, migraine, and possibly transient ischemia of the hippocampus on one or both sides.

Bedside Tests of Memory and Cognitive Function

The MMSE consists of 30 points: The low-normal cutoff is estimated

to be 19 for uneducated people, 23 for graduates of elementary or junior high school, 27 for high school graduates, and 29 for college graduates.