Left+Frontal+Lobe

Injury/Damage:
-Depression -"psycho-motor" retardation -Tearfulness -Apathy -Irritability -Blunted intellectual and conceptual capability -Confusion and a reduced ability to appreciate and appropriately respond to the external or internal environment -Puerility (silliness, childishness) -Either total or partial unawareness of the environment. -S ometimes characterized as suffering from an emotionally blunted form of schizophrenia
 * left lateral and medial frontal lobe: **

-Disconnection between cognitive-perceptual and emotional activity -Prevention of limbic system output from reaching the motor areas, thus motorically hypo-emotionally aroused (i.e. depressed), and appears to be demonstrating psychomotor retardation. -Emotional output from the right hemisphere and limbic system fail to become integrated with linguistic-ideation (i.e. thought) so ideas no longer come to be assigned emotional significance. -In the extreme the motivational impetus to even engage in thought production is cut-off.
 * Convexity lesions, e.g. medial damage: **

-difficulty with expressive speech -Become exceedingly frustrated, irritable, and depressed
 * Broca's area: **

With severe injuries, instead of worried or emotionally depressed, the patient instead is indifferent, uncaring, apathetic, and emotionally blunted.
 * Severe damage: **

**DEPRESSION IN LEFT FRONTAL LOBE INJURY**
In large part, depression is common with Broca's aphasia as patients are painfully aware of their deficit. Those with the smallest frontal convexity lesions often become the most depressed. Depression in these cases appears to be a normal reaction and as such is mediated by undamaged tissue; i.e., the right hemisphere which is dominant for emotional expression and perception. The right hemisphere being emotionally astute, reacts appropriately to the patient's condition and becomes depressed. Almost all other studies demonstrate increased right frontal activity in response to negative moods and decreased left frontal activity with depression. In fact, repetitive transcranial magnetic stimulation of the right frontal lobe reduces depressive symptoms, whereas left frontal activity increase with the alleviation of depression.

Psychiatric patients classified as depressed, and normal individuals made to feel severely depressed, demonstrate insufficient left frontal activation and arousal Depressed mothers and depressed children show reduced left relative to right frontal activation. With recovery from depression left hemisphere arousal returns to normal levels. Likewise, Patients who are severely depressed have been shown to demonstrate insufficient activation and a significant lower integrated amplitude of the EEG evoked response over the left vs right frontal lobe. Functional imaging of depressed states indicates reduced activity in the left frontal lobe and anterior cingulate and when these individuals ceased to be depressed, activity levels increases.

Depressive-like features, however, also seem to result with left anterior damage sparing Broca's area such as when the frontal pole (of either hemisphere is compromised. In some, this initial state of inertia disappears, whereas in others it becomes a lasting or even progressively severe disturbance.

In part, depression coupled with apathy secondary to frontal injuries is probably related to damage to the interconnections with the medial region, an area which when damaged induces hypokinetic and apathetic states. However, these latter patients are not depressed, but rather severly apathetic, indifferent, hypoactive, and poorly motivated. When questioned, rather than worried or truly concerned about their condition the overall picture is that of confusion, disinterest, and blunted emotionality i.e. there is a lack of worrisome thoughts or depressive ideation.

Hence, in part, apathetic and depressive features may result from left frontal convexity and frontal pole damage due to a severance of fibers which link emotional impulses (such as those being transmitted via the orbital and medial region) with external sources of input or cognitive activity which are transmitted to the convexity (i.e. disconnection), impulses which are transmitted from the medial frontal lobes to the orbital, superior, and anterior frontal lobes. Through these interconnections, emotional impulses arising in the limbic system, can be transmitted through the medial frontal lobes to the lateral frontal lobes, where they then become ideas. Or conversely, neocortical cognitions may be transmitted from the lateral neocortical surface to the medial areas where they are integrated to again become emotional ideas.

Patients classified as schizophrenic have also been reported to demonstrate abnormal left( or bilateral) frontal lobe EEG's indicative of hypoarousal. Lateral frontal gray matter and brain volume reductions and decreased activity have been repeatedly noted, including decreased blood flow, hypoactivity, reduced metabolism, as well as left sided abnormalities affecting the striatum.
 * THE LEFT LATERAL FRONTAL LOBE & STRIATUM: SCHIZOPHRENIA PSYCHOSIS & BLUNTED (NEGATIVE) SCHIZOPHRENIA **

This is not to imply that all subtypes of "schizophrenia" are secondary to frontal lobe pathology. The left temporal lobe have also been implicated, however, as the //temporal lobes// are implicated in these subtypes of schizophrenia, the pattern of symptoms differs from those with left frontal dysfunction.
 * Differential Dx**

For example, depending on if the right vs left and superior vs the inferior temporal lobe are more greatly impacted, patients are more emotional, more verbal, more active, and more likely to suffer visual and auditory hallucinations, coupled with disturbances of comprehension. However, whereas as a superior temporal lobe (Wernicke's area) abnormality can affect the left frontal lobe (Broca's area) thus producing fluent-aphasic speech and thus a complete formal thought disorder, left inferior temporal lobe and amygdala dysfunction can disrupt the orbital and medial frontal lobe including the caudate and putamen.

Only certain subpopulations of schizophrenics actually suffer from //frontal lobe// dysfunction, such as those with -Catatonia -Posturing -Mannerisms -Emotional blunting coupled with reduced speech output and apathy. -Not all "frontal" schizophrenics are blunted, but may display unusual mannerisms and/or a silly, puerile childishness that used to be referred to as "Hebephrenia"

LEFT FRONTAL DEVELOPMENTAL DOMINANCE FOR MOTOR FUNCTIONS
The motor cortex of the left hemisphere is dominant for motor control; a function of the earlier maturation of the left cerebral motor areas and the descending corticospinal tract. In most people the nonmotor areas of the right frontal lobe appear to initially develop more rapidly than the left, which in turn enables the right hemisphere to gain dominance over sensory limbic functions. By contrast, the primary somatomotor areas of the left frontal lobes mature at a more rapid rate than the right frontal lobes and by the first year tissues take over their right sided counterparts.

Due to early left hemispheric motor development, the left corticospinal tract grows more quickly and descends into the brainstem, and then crosses at the pyramidal decussation, and then descends into the spinal cord in advance of those fibers from the right. This provides the left hemisphere and the right hand with a competitive advantage in establishing both motor control and thus right hand dominance.
 * Right vs. Left Hand dominance **

At //8-12 months// of age the following changes occur: <span style="font-family: 'Times New Roman',serif;">-The corticospinal tract begins to reach advanced levels of myelination and become functionally mature - it is only as the infant approaches their first birthday that handedness become obvious or apparent. -M<span style="font-family: 'Times New Roman',serif;">otor and somatosensory areas become increasingly mature and the secondary motor and sensory receiving areas display increased myelination -F<span style="font-family: 'Times New Roman',serif;">rontal lobes increase metabolic activity and begins to increasingly resemble a more adult pattern <span style="font-family: 'Times New Roman',serif;">-Corticospinal and pyramidal axons begin to approximate adult level of cellular development, myelination, and organization, and then become increasingly well myelinated over the course of the second year -a process which continues into late childhood. <span style="font-family: 'Times New Roman',serif;">-The neocortex and frontal motor areas hence begin to increasingly exert hierarchical control over the limbic forebrain, brainstem, and musculature, and this process continues to develop over the course of the ensuing decade and requires considerable coordinated interaction between the parietal and motor areas of the frontal lobe as well as the striatum, limbic system, and cerebellum.