Functional Neuroanatomy: Frontal Lobes

Functional Neuroanatomy: Frontal Lobes Anatomy and Functional Organization: General Statements: Last to develop, sometime not until early adulthood. Age 18 to 21. Although some research suggests now is much later, early twenties. 1/3 of the mass of the brain. Allow us to function as effective and socially appropriate individuals. Very heterogeneous and difficult to study.

Functional Neuroanatomy: Frontal Lobes Lesions may produce highly variable behaviors. Rich connections with all other regions of the brain. Major structures: Primary Motor Supplemental Motor Premotor Frontal Eye Fields Prefrontal Basomedial (orbitofrontal)

Functional Neuroanatomy: Frontal Lobes

Functional Neuroanatomy: Frontal Lobes Primary Motor Area: Located on precentral gyrus. Rate of firing correlated with force. Somatotopic organization. Feet up high. Head down low. Motor homunculus: Some regions of body have more representation that others. Hence your body is distorted on your brain. You don’t look like what you really look like!

Functional Neuroanatomy: Frontal Lobes What do you notice here? Variable representation?

Functional Neuroanatomy: Frontal Lobes

Functional Neuroanatomy: Frontal Lobes Lesions: Fine movements, speed, and strength. Chronic loss of ability to make fine, independent finger movements. Loss of motor speed. Strength as well, all contralateral to side of lesion.

Functional Neuroanatomy: Frontal Lobes Supplemental Motor Area: Medial and some lateral aspect of cortex. Reciprocal connections to primary motor, premotor, and somatosensory. Important for the temporal organization of movement. Especially sequencing of multiple movements. And in tasks that require retrieval of motor memory. Programming: Integration of:

Functional Neuroanatomy: Frontal Lobes External input. Commands. Stimuli. With internal drives and needs. Facilitates and formulation of movement strategy. Lesions: May produce contralateral akinesia – global reduction in movement. Deficits with rapid alternating movements. Grasp reflex.

Functional Neuroanatomy: Frontal Lobes Premotor: About 6x larger than primary motor. Anterior to the precentral gyrus, i.e. primary motor. Voluntary motor programming in coordination with sensory inputs (visual, auditory, somatosensory). Stimulation yields stereotyped gross movements, such as: Movement of head, eyes, trunk. Contralaterally.

Functional Neuroanatomy: Frontal Lobes Influences movement through connections with primary motor area. Selection of which movements to perform. Lesions: Deficit in skilled, sequential, complex movement. Such as walking. Apraxia. But, in the absence of plegia or paralysis. Frontal eye fields: Dorsolateral frontal, middle frontal gyrus.

Functional Neuroanatomy: Frontal Lobes Triggers voluntary saccades to: Visible targets in contralateral hemispace. Remembered target locations. Predicted target locations. Differing effects of stimulation versus ablation: Stimulation: On left yields eyes to the right. On right yields eyes to the left. Ablation: On left yields eyes to the left. On right yields eyes to the right.

Functional Neuroanatomy: Frontal Lobes Test using Trail Making Test. Also eye movements away from stimulus. Prefrontal: All the rest of the area? Motor responses not necessarily ruled out with stimulation. Important in affective and judgmental behaviors. Extensive connections with: Hypothalamus Medial thalamus Amygdala

Functional Neuroanatomy: Frontal Lobes Receives input from all the senses. Important for goal directed behaviors: Motivation. Motor Movements: Motor cortex for making movements. Premotor for selecting movements Prefrontal for controlling cognitive processes involved in ensuring that right movements are selected at the right time and place. Memory: Working memory:

Functional Neuroanatomy: Frontal Lobes Involves some sort of manipulation. Bilateral frontal. Intentional memory: Forgetting to remember. Short-term memory: Temporal memory – neural record of recent events. Retrieval processes. Perseverative behaviors: Can’t alter responses when stimulus changes. WCST Lawnmower man

Functional Neuroanatomy: Frontal Lobes Impulsivity and delayed response deficits: Right – too fast Left – too slow Language: Left Frontal: Verbal fluency. Broca’s aphasia or expressive aphasia. Right Frontal: Nonverbal fluency. Expressive aprosodia.

Functional Neuroanatomy: Frontal Lobes Planning and problem solving: Difficulty completing tasks or doing tasks that require multiple subgoals. Emotion: Expression of emotion: Positive on left Pathological laughter. Negative on right Pathological crying. Right Frontal may yield anosognosia. Depression follows left frontal dysfunction. Closer to frontal pole the more severe.

Functional Neuroanatomy: Frontal Lobes Anxiety: Left frontal characterized by excessive worry. Right frontal characterized by panic attacks. Consider case of Phineas Gage: Previously was a foreman. After accident couldn’t be. Ill tempered. Profanity. Emotional lability. Poor judgment.

Functional Neuroanatomy: Frontal Lobes

Functional Neuroanatomy: Frontal Lobes Lesions: Problems with inhibition. Distractible. Apathy, lack of “get-up-and-go” and initiative, i.e. abulia. Surgical ablation in past for mental disorders. And intractable pain – doesn’t “feel” as bad. Arousal and activity: Left yields decreased arousal, slowness. Right yields increased activity, arousal, ADHD. Apathy, as with anosodiaphoria. Socially inappropriate behaviors, especially with right: Crude jokes.

Functional Neuroanatomy: Frontal Lobes Laugh inappropriately. Overly erotic. Disinhibition. Memory: Retrieval deficits. Source amnesia. Temporal memory – what occurred first. Orbitofrontal: Involved in emotions and control of inhibition. Changes in mood and affect. Such as hostility.

Functional Neuroanatomy: Frontal Lobes Socially inappropriate. Additional Frontal Lobe Signs and Symptoms: Remember, frontal lobes are the brakes. Reflexes: Myerson Sign Grasp Rooting With memory, variable responses per trial on list-learning.

Functional Neuroanatomy: Frontal Lobes Increased sensitivity to light, touch, sound. May also see exaggerated startle response. Visuoconstructive Tasks: Deficits arise from poor organization. Cannot integrate. Arithmetic Problem Solving: Problems with questions involving multiple steps. Speech: Broca’s area: Involved in selection of words to use. On the basis of the object, word, or meaning.

Functional Neuroanatomy: Frontal Lobes Lesion at Broca’s: Impaired ability to use verbs. Use of inappropriate grammar, agrammatism. Reduced fluency as well. Reduced performance on COWAT.