TEMPORAL LOBE ANATOMY, FUNCTION & EVALUATION

DR. PIYUSH OJHA

DM RESIDENT

DEPARTMENT OF NEUROLOGY

GOVT MEDICAL COLLEGE, KOTA

ANATOMY• Percentage of Temporal lobe:total cerebral cortex volume in humans: 22%

• The Temporal Lobe contains all the tissue in the brain that lies below the Sylvian (Lateral) fissure and anterior to the Occipital cortex.

• Subcortical Temporal lobe structures include –

- Limbic cortex

- Amygdala

- and Hippocampal formation.

• Connections to and fro from the temporal lobe extends throughout the brain.

• Has 2 sulci that run parallel to the posterior ramus of the lateral sulcusnamed Superior and Inferior temporal sulci.

• These sulci divide the superolateral surface of temporal lobe into Superior, Middle and Inferior Temporal Gyri.

• Temporal lobe includes-1. superior, middle & inferior temporal convolutions

2. lateral occipitotemporal convolutions

3. fusiform convolutions

4. lingual convolutions

5. parahippocampal and hippocampal convolutions

6. Transverse gyri of Heschl (PRIMARY AUDITORY RECEPTIVE AREA)

• Brodmanm areas on lateral suraface

of Temporal lobe –

- Auditory area (area 41, 42)

- Auditory association cortex (area 22)

- Ventral visual stream areas

( area 20, 21, 37 & 38 )

The Medial Temporal region (LIMBIC CORTEX) includes :-

- Amygdala and adjacent cortex (Uncus )

- Hippocampus and the surrounding cortex i.e. - Subiculum - Entorhinal Cortex (Brodmann area 28 )- Perirhinal Cortex (Broadmann area 35 & 36 )

BLOOD SUPPLY OF TEMPORAL LOBE

• Convexity – inferior branch of MCA

• Medial & inferior aspects (including Hippocampus) – temporal branch of PCA

SUPERIOR TEMPORAL LOBE

• This is bounded by:

- the lateral sulcus above;

- the superior temporal sulcus below;

• It contains several important structures including:

- Brodmann areas 41 and 42, marking the location of the Primary auditory

cortex, known as Transverse temporal gyri (also called Heschl's gyri)

- Wernicke's area, Brodmann 22

MIDDLE TEMPORAL LOBE

The region encompasses most of the lateral temporal cortex, a region believed to

play a part in auditory processing and language.

- Language function is left lateralized in most individuals.

- Brodmann area 21.

INFERIOR TEMPORAL LOBE

• In humans it corresponds approximately to the inferior temporal gyrus.

• Brodmann area 20.

• The region encompasses most of the ventral temporal cortex, a region believed to play a part in high-level visual processing and recognition memory.

AMYGDALA

•The amygdala (Latin,meaning'almond') are almond-shaped groups of neurons located deep within the medial temporal lobes of the brain, in close relation to anterior end of inferior horn of lateral ventricle, located at anterior end of hippocampal formation.

The Hippocampus

- The hippocampus is a scrolled structure located in the medial temporal lobe.

- can be divided into at least 5 different areas.

- Areas CA3 and CA1 are more diffuse; CA2 is hard to distinguish between them.

- (CA stands for cornu ammonis, from its

ram's horn shape.)

- The subiculum sits at the base of the hippocampus, and is continuous with entorhinal cortex, which is part of the parahippocampal gyrus.

Dentate gyrus• Part of the hippocampal formation.

• Contains granule cells, which project to the pyramidal cells and interneurons of the CA3 subfield of the hippocampus.

• The granule cells are the principal excitatory neurons of the dentate gyrus.

• The major input to the dentate gyrus (Perforant pathway) is from the entorhinal cortex, and the dentate gyrus receives no direct inputs from other cortical structures.

• The dentate gyrus is also one of the few regions of the brain where neurogenesis takes place. Neurogenesis is thought to play a role in the formation of new memories.

Connections of the Temporal Lobes-

Five main types:

1. Hierarchical sensory pathway

2. Dorsal auditory pathway

3. Polymodal pathway

4. Medial (mesial) temporal pathway

5. Frontal lobe projection

Hierarchical sensory pathwayconnections from primary and secondary auditory

and visual cortical

through the lateral temporal cortex

terminate in the temporal pole

• Subserves stimulus recognition

Dorsal auditory pathway

• Forms important functional connections from auditory areas to posterior parietal cortex

• Concerned with directing movements with respect to auditory information

Polymodal Pathway

• A series of parallel projections from the visual and auditory association areas into the polymodal regions of the superior temporal sulcus

• Functions in stimulus categorization

Medial Temporal Projection

• Projections from auditory and visual areas into the limbic regions

E.g., amygdala and hippocampus

• Also called Perforant pathway

• Serves function in long term memory

Frontal-lobe Projection

• Auditory and visual information goes to two prefrontal regions, one on the dorsolateral surface and the other in the orbital region

• necessary for various aspects of movement control, short-term memory and affect.

Temporal Lobe Function

• Three Basic Sensory Functions :

– Processing auditory input

– Visual object recognition

– Long-term storage of sensory input (Memory)

Temporal Lobe Function

• Sensory Processes

– Identification and Categorization of Stimuli

– Cross-Modal Matching

• Process of matching visual and auditory information

• Depends on cortex of the superior temporal sulcus

• Affective Responses

– Emotional response is associated with a particular stimulus

• Spatial Navigation

– Hippocampus – Spatial Memory

Superior Temporal Sulcus (STS) and Biological Motion

• Functional Imaging reveals activation in the STS during perception of Biological motion.

• Biological Motion

– Movements relevant to a species , Social perceptions

– Allow us to guess others’ intentions

FUNCTIONS OF TEMPORAL LOBE

Consider an example..

• Imagine that you want to buy a car and now you are riding a two wheeler. On your ride, you notice many different cars, and you decide to keep a mental list of the brands and coloursthat you encounter so that you can discuss with family and friends later on.

• As you ride along, you suddenly stop and back up—you have encountered a traffic policeman on the roadside of the next square walking with a fineslip towards you . You decide to change routes and look for cars elsewhere!

• What temporal-lobe functions took part in your experience?

• To be aware of specific type, colour and brand- object recognition by ventral visual pathway

• To categorize quickly as they are in motion-polymodalpathway in superior temporal sulcus

• Matching acceleration/engine sound to visual input- Cross modal matching by dorsal auditory pathway

• Policeman walking towards you- “Biological motion” by superior temporal sulcus

• On seeing fineslip- increased HR and BP and affective response- by amygdala

• To change route and search elsewhere (spatial orientation)-hippocampus

• To remember all the cars and discuss- medial temporal lobe

TEMPORAL LOBE FUNCTIONS

• SPECIAL SENSES

– Hearing

• FUNCTIONS OF LIMBIC SYSTEM

– Memory

– Emotions & Mood

– Attitudes & Social Behaviour

• LANGUAGE FUNCTIONS

– Semantics

– Naming

• VISUAL & OTHER SENSORY INTEGRATION

HEARING

• Auditory cortex lies principally on the supratemporal plane of superior temporal gyrus (Heschl’s gyrus)

• Primary cortex has tonotopic arrangement:

– high tones terminate in medial portion

– Low tones in lateral portions

• Particular sound frequency causes excitation of particular cortical area =sound frequency perception

• Also helps in discrimination of sound patterns like combination or sequence of tones

• Also takes part along with superior olivary nucleus in mechanism for detecting sound direction

HEARING

Nondominant hemisphere- non-verbal aspect, recognition of harmony & melody

Dominant hemisphere- verbal aspect,naming of musical scores & all the semantic (writing, reading)

aspects of music

LIMBIC SYSTEM FUNCTION

• Coordinate sensory events with bodily and visceral needs

• Regulate innate automatised activities concerned with feeding, searching, sex, & emotion-provoking situations

• Neurotransmitters:

– For memory- acetyl choline

– Norepinephrine in medial parts of limbic system

– Amygdala, septal nuclei & lateral parts are rich in serotonin

TEMPORAL LOBE/LIMBIC SYSTEM:FUNCTION

• Limbic system regulates emotions and motivations—particularly those related to survival—such as fear, anger, and pleasure (sex and eating)

• Feelings of pleasure/reward are very powerful and self-sustaining. Pleasurable behaviors activate a circuit of specialized nerve cells in the limbic area that is devoted to producing and regulating pleasure called the reward system

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Emotion and Motivation(Individual function)

Rage, aggression Amygdala and hypothalamus.

Fear Amygdala and hypothalamus

Feeding Hypothalamus (satiety centers).

Sexual drive and behaviorHypothalamus and limbic system

Goal directed behavior (reward and punishment):

Hypothalamus and frontal cortex

MEMORY-Medial temporal lobes

• The MTL is comprised of multiple structures including the

• This is involved in explicit or declarative memory.

• It has essential role in the formation of new memories about experienced events (episodic or autobiographical memory).

Hippocampal formation, Amygdala, Entorhinal cortex, and Surrounding perirhinal and parahippocampal cortices

Memory : HIPPOCAMPUS

• Critical in laying down declarative memory, but is not necessary for working memory / procedural memory / memory storage.

• The hippocampal formation plays a role in memory consolidation

• Damage to the hippocampus usually results in profound difficulties in forming new memories (anterograde amnesia), and normally also affects access to memories prior to the damage (retrograde amnesia) but does not affect procedural memory

Memory : Parahippocampal cortex

•Sensitive to familiarity with stimulus location or the geometry of surrounding space

•Patients with a lesion limited to parahippocampal cortex lose the ability to acquire new topographic knowledge

•The Parahippocampal Area responds selectively to visual stimuli that convey information about the layout of local space.

Emotional learning

Amygdala perform primary roles in the formation and storage of memories associated with emotional events

WERNICKE’S AREA

• The sensory area of the dominant hemisphere for interpretation of language is Wernicke’s area.

• Closely associated with hearing areas

• Provides, at the input stage, an entry point for conversion of auditory sequences into neural word representations leading to meaning-appropriate content words.

• Localization of lexicon (vocabulary ) for spoken word recognition exists in middle part of left superior & middle temporal gyri

• Lexicon for written word recognition exists in posterior part of left middle temporal gyrus

• A major share of our sensory experience is converted into language equivalent before stored in memory areas

WERNICKE’S AREA

Reception in primary auditory area of sound signals that encode words

Interpretation of words in Wernicke’s area

Determination of thoughts & words to be spoken in Wernicke’s area

Transmission of signals form wernicke’s area to Broca’s area by arcuate fasciculus

Activation of skilled motor programs in Broca’s area for control of word formation

Transmission of appropriate signals into motor cortex to control speech muscles

Primary visual area is the initial receptive area

Early stage of interpretation in angular gyrus

Full level of recognition in Wernicke’s area

Hearing & speaking Reading & speaking

VISUAL INTEGRATION

• Middle & inferior temporal gyri (areas 21 & 37) receive massive contingent fibers form striate cortex (area 17) & parastriate visual association areas (areas 18,19)

• Subserves visual discriminative functions like spatial orientation, estimation of depth & distance, stereoscopic vision, & hue perception

• It integrates vision intimately with all forms of exteroception & proprioception

• Bitemporal lobectomy in animals-‘psychic blindness’

SENSORY INTEGRATION

• Temporal lobe is great integrator of ‘sensations, emotions and behaviour’

• It is the site where sensory modalities are integrated into ultimate self-awareness

• Similar suprasensory integrative mechanisms are operative in parietal lobe, but only in the temporal lobe are they brought into close relationship to one’s instinctive & emotional life

• Stream of thinking (internal conversation that is constant in waking state) requires language & memory functions, both of which involve temporal lobe

• Temporal lobe throughout the life assembles all fragments of present & past experiences of all kinds into awareness of personal integrity which is only interrupted by sleep

• Temporal neocortex functions to bring ultimate awareness that ‘I am’.

OTHER FUNCTIONS

• Vestibular functions:– Some fibers from vestibular input are relayed in superior temporal

gyrus

– Episodic vertigo may represent the aura or sole manifestation of temporal CPS

• Time perception:– Main neural mechanism subserving time perception & integrating it

with other sensory inputs and memory lies in temporal lobe

– With disorder of temporal lobe of either side, there may be intermittent disturbance of time perception

Symptoms of Temporal Lobe Lesions

Symptoms of Temporal Lobe Lesions

1. Disturbance of Auditory Sensation and perception

2. Disorders of music perception

3. Disorders of visual perception

4. Disturbance in the selection of visual and auditory input

5. Impaired organization and categorisation of sensory input

6. Inability to use contextual information

7. Impaired long term memory

8. Altered personality and affective behavior

9. Altered sexual behavior

Disturbance of Selection of Visual and Auditory Input

• Selective attention to auditory input is impaired in patients with temporal lobe damage and can be tested with dichotic listening

• Damage to the left temporal lobe impairs recall of visual stimuli in the right visual field

• Damage to the right temporal lobe impairs recall of visual stimuli in both visual fields

Organization and Categorization

• Left temporal lobe lobectomies lead to impairment in the ability to categorize words or pictures of objects

• Posterior lesions lead to a difficulty in recognizing specific word categories

Using Contextual Information

• Stimuli can be interpreted in different ways depending on the context

– Example: Fall - the season or a tumble

Memory

• Antereograde Amnesia– Amnesia for events after bilateral removal of the medial

temporal lobes

• Inferotemporal Cortex– Conscious recall of information

• Left temporal lobe– Verbal memory

• Right temporal lobe– Impaired recall of nonverbal material

Affect and Personality

• Stimulation of anterior and medial temporal cortex produces feelings of fear

• Temporal lobe personality

– Personality that overemphasizes trivial and petty details of life

– Pedantic speech (an overly formal speaking style inappropriate to the

conversational setting)

– Egocentricity (preoccupation with one’s own internal world)

– Perseveration

– Paranoia

– Preoccupation with religion

– Proneness to aggression

Changes in Sexual Behavior

• Release of sexual behavior seen after bilateral temporal damage

Superior temporal Gyrus

• Auditory radiations run from the medial geniculate body to the Auditory cortex ( areas 41 and 42) in the superior temporal gyrus.

• Hearing is represented bilaterally in the temporal lobes.

(contralateral predominance)

• Nearby areas - differentiation and interpretation of sounds.

• Electrical stimulaton of auditory area leads to vague auditory hallucination (tinnitus, sensation of roaring and buzzing ), and adjacent areas causes vertigo and a sensation of unsteadiness.

• Unilateral destruction of the Auditory cortex lead to difficulty in sound localisation and a bilateral decrease of auditory acuity.

• Bilateral disease lead to Cortical deafness (may be unaware of their deficits).

• Audiometric tests may be helpful to reveal mild deficits.

• Involvement of vestibular areas may cause difficulty in equillibrium and imbalance

Asymmetry of Temporal lobe function

• Damage to left temporal lobe – deficits in verbal memory, processing

speech sounds

• Damage to right temporal lobe – deficits in nonverbal memory

processing certain aspects of music

face recognition

TESTING OF TEMPORAL LOBE

Dichotic listening task

TESTS FOR VISUAL PROCESSING

Verbal memory

• Revised Wechsler Memory Scale- seven subtests:

Spatial Addition, Symbol Span, Design Memory, General Cognitive Screener, Logical Memory(I & II), Verbal Paired Associates(I & II), and Visual Reproduction(I & II).

• A person's performance is reported as five Index Scores: Auditory Memory, Visual Memory, Visual Working Memory, Immediate Memory, and Delayed Memory

Non verbal memoryRey Complex Figure

Non verbal memory (e.g.,)

TEMPORAL LOBE SYNDROMES

Homonymous upper quadrantanopia

Wernicke’s aphasia

Amusia

Anomia

Visual agnosia

Impairment on tests of visually presented material

Homonymous upper quadrantanopia

Agnosia for sounds & some qualities of music

Impairment on tests of visually presented material

U/L disease of dominant lobe U/L disease of nondominant lobe

TEMPORAL LOBE SYNDROMES

Auditory, visual, olfactory & gustatory hallucinations

Dreamy states

Emotional & behavioural changes

Delirium

Disturbance of time perception

Korsakoff amnesic defect

Apathy & palcidity

Hypermetamorphopsia, hyperorality, hypersexulaity, blunted emotional reactivity (Kluver-Bucy syndrome)

Either temporal lobe Bilateral disease

Wernickes Aphasia

• Also known as Fluent / Recepetive / Sensory / Postrolandic Aphasia• Due to destruction of posterior superior temporal area of the dominant

hemisphere supplied by inferior division of MCA.– Fluency is preserved with a normal or even increased word

output (LOGORRHEA)– Speech although effortless is devoid of meaningful content– Paraphasias, Neologisms and defective sentence structure

(PARAGRAMMATISM) (JARGON APHASIA)– Auditory comprehension is impaired, even unaware of his own

speech, and doesnot correct himself.– Repetition impaired– Reading impaired– Naming impaired– Writing impaired– Patient often is unaware of the defect

Temporal lobe epilepsy / psychomotor seizures

• Patients with Temporal lobe lesion may have visual hallucinations and perversions.

• Visual hallucinations are complex with image distortion (macropsia / micropsia / near / far )

• May have an auditory component

• Lesions involving medial temporal lobe in the region of Uncus ( so also k/a UNCINATE FITS which involve olfactory hallucination also)

• Seizures may present as : automatisms, illusions and hallucinations , and pilomotor erections.

• Amnesia for the event is usually seen.

• DÉJÀ VU ( already seen), JAMAIS VU (something familiar is strange or new), DEJA PENSEE/ DEJA VACU ( something new seeming strangely familiar) , EXPERIENTIAL HALLUCINATIONS (Hallucinations based on remembered experiences)

KLUVER- BUCY SYNDROME

• Experimentally due to bilateral ablation of temporal lobes in monkeys.

• Placidity i.e. extreme calmness

• Lack the ability to visually recognize objects.

• Striking tendency to put everything into mouth.

• Hypersexuality

• Increased food intake

• Seen only in partial forms in humans ( placidity and enhanced oral behavior are the most common presentations)

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