lobes&Functions

1. Frontal Lobe

* General Functions: Memory formation, decision making, reasoning, personality, emotions, goal attainment.

* Area 4 (Primary Motor Cortex - Precentral Gyrus):

   * Function: Direct control of voluntary motor movements across specific body parts (arranged as the motor homunculus).

   * Lesion: Contralateral flaccid paralysis/paresis (progressing to spasticity/upper motor neuron signs).

* Area 6 (Premotor Cortex & Supplementary Motor Area):

   * Function: Motor planning, elaboration of thoughts, and coordination of complex movement sequences.

   * Lesion: Motor apraxia (inability to carry out purposeful movement despite normal strength).

* Area 8 (Frontal Eye Field):

   * Function: Controls voluntary conjugate horizontal eye movements to the opposite side.

   * Lesion: Conjugate eye deviation toward the side of the lesion (inability to gaze toward the opposite side).

* Areas 44 & 45 (Broca’s Area - Dominant Left Frontal Lobe):

   * Function: Word formation, speech production, motor pattern planning for individual word expression.

   * Lesion: Expressive (Broca’s/motor) aphasia — non-fluent speech, slow/labored utterance, decreased motor ability to form words, but preserved comprehension.

* Prefrontal Association Area (Anterior Pole of Frontal Lobe):

   * Function: Planning complex patterns of movement, personality development, social behavior, deep/abstract/logical thinking, working memory (comparing inputs with stored knowledge for future plans).

   * Lesion: Personality and behavioral changes, impaired logical reasoning, poor judgment/decision-making (e.g., Phineas Gage case).

* Olfactory Bulb (CN I) & Orbitofrontal Cortex:

   * Function: Sensation and perception of smell.

2. Parietal Lobe

* General Functions: Senses and integrates tactile sensations, spatial awareness, proprioception (awareness of body parts in space).

* Areas 3, 1, 2 (Primary Somatosensory Cortex - Postcentral Gyrus):

   * Function: Processing tactile, pain, thermal (warmth/cold), and proprioceptive inputs (arranged as the sensory homunculus).

   * Lesion: Contralateral loss of sensory discrimination, tactile localization, two-point threshold, and contralateral sensory inattention.

* Area 43 (Primary Gustatory Cortex):

   * Function: Primary site for perception and interpretation of taste.

   * Lesion: Loss of taste sensation (ageusia) on the ipsilateral side of the tongue.

* Areas 5 & 7 (Somatosensory Association Cortex):

   * Function: Integrates and interprets sensory inputs relative to body position/orientation in space, stereognosis, visuo-motor coordination.

   * Lesion: Astereognosis (inability to recognize complex shapes/objects by palpation/touch) and hemispatial neglect syndrome.

3. Temporal Lobe

* General Functions: Hearing, organization/comprehension of language, information retrieval (memory formation).

* Areas 41 & 42 (Primary Auditory Cortex - Heschl's Gyri):

   * Function: Primary reception and processing of auditory stimuli and pitch.

   * Lesion: Bilateral lesions cause central deafness; unilateral lesions cause mild hearing loss with difficulty localizing sound source.

* Area 22 (Wernicke’s Area - Superior Temporal Gyrus, Dominant Left Hemisphere):

   * Function: Language comprehension, intelligence, higher intellectual functions, word organization.

   * Lesion: Receptive (Wernicke’s/sensory) aphasia — fluent but meaningless speech ("word salad"), poor comprehension, lack of awareness of defects, memory impairment, temporal lobe epilepsy.

* Primary Olfactory Cortex:

   * Function: Direct cortical interpretation of smell received via olfactory bulbs.

4. Occipital Lobe

* General Functions: Visual processing, integration, interpretation of visual stimuli.

* Area 17 (Primary Visual Cortex - Calcarine Sulcus):

   * Function: Primary site responsible for sight (recognition of size, color, light, motion, dimensions).

   * Lesion: Contralateral homonymous hemianopia (with macular sparing in PCA infarctions sparing MCA territory).

* Areas 18 & 19 (Visual Association Cortex):

   * Function: Interprets and integrates visual information acquired through the primary visual cortex.

   * Lesion: Visual agnosia and color agnosia.

5. Multimodal Association Areas & Specialized Regions

* Parieto-Occipitotemporal Association Area:

   * Spatial Coordinates Computation (Posterior Parietal to Superior Occipital): Computes coordinates of visual, auditory, and surrounding spatial environment.

   * Angular Gyrus (Visual Language / Reading): Processing visual language to derive meaning from written words.

     * Lesion: Alexia / Word Blindness.

   * Area for Naming Objects (Lateral Anterior Occipital & Posterior Temporal): Naming recognized objects.

* Limbic Association Area (Anterior & Inner Portion of Temporal Lobe):

   * Function: Emotional expression, behavior, motivational drive for tasks, learning.

   * Lesion: Decreased aggression, lack of emotion, hypersexuality, hyperphagia.

* Facial Recognition Area (Fusiform Area - Medial Underside of Occipital & Temporal Lobes):

   * Function: Recognizing human faces (occipital side connects to visual cortex; temporal side connects to limbic system).

   * Lesion: Prosopagnosia (inability to recognize faces).

6. Cortical Microarchitecture & Hemispheric Specialization

* 6 Layers of Cerebral Cortex (Outside \rightarrow Inside):

   * Layer I (Molecular) & Layers II/III (External Granular/Pyramidal): Perform intracortical association functions via short horizontal connections.

   * Layer IV (Internal Granular): First destination for incoming sensory signals from thalamus.

   * Layer V (Large Pyramidal): Sends motor output signals to brainstem and spinal cord.

   * Layer VI (Fusiform/Polymorphic): Sends output signals back to thalamus.

* Hemispheric Specialization:

   * Left (Dominant Hemisphere in ~90%): Language, speech, reading, writing, mathematics, logic, decision-making.

   * Right (Non-Dominant Hemisphere): Music appreciation/interpretation, non-verbal visual experiences, spatial relationship perception, body language, voice intonation.