Attention+and+Neglect

The parietal lobes are heavily involved in directing and maintaining various aspects of motoric, visual and somesthetic attentional functioning. This includes the maintainance of visual fixation, the guidance of hand and manipulatory activities, or the detection and monitoring of a stimulus moving across the body surface. In part, this is accomplished via interconnections with the various association areas, frontal lobes,the superior colliculus and the reticular formation --all of which are heavily involved in attention and/or arousal.
 * ATTENTION & NEGLECT**

//Laterality//: Right and left parietal lobes do not exert identical or equal influences. Ex: many neurons in the secondary somesthetic areas receive contralateral and ipsilateral input whereas many visual neurons in area 7 are bilaterally responsive appears to be more characteristic of the right parietal region. The right seems to contain a greater number of bilateral cells. Thus, visual and somesthetic stimuli exert greater EEG evoked responses over the **right half of the brain and the right cerebral hemisphere** becomes activated by stimuli applied to the right or left half of the body. Conversely, the **left hemisphere** becomes aroused predominantly in response to unilateral (right sided) input.

Reaction times to visual stimuli are also more greatly reduced following right vs. left cerebral injuries. Similarly, among split-brain patients, the right cerebral hemisphere is able to maintain attention for appreciably longer time periods, whereas the left hemisphere tends to demonstrate attentional lapses as well as unilateral spatial-conceptual neglect. Accordingly, tasks of sustained motor-visual attention performance in the left half of space (with either hand) is superior to the right half of space.

Lesions or surgical removal of the right parietal lobe (particularly the inferior regions extending into the second occipital convolution or the frontal lobe), can results in unilateral neglect of the left half of visual, somesthetic and auditory space. In the extreme, these patients may fail to become consciously aware that half the body is in some way dysfunctional, or even that it exists. They may dress or groom only the right half of their body, eat only off the right half of their plates, etc or, when conjuring up mental imagery, i.e. the left half of the image disappears. As attention may be directed to at least three dimensions of visual space, radial, vertical, horizontal, including near and far peripersonal space, effected individuals may show neglect only the lower quadrants -the domain of the parietal lobes- or in the upper quadrants -the domain of the temporal lobe.

Neglect may take the form of hypoarousal or inattentiveness and may involve different modalities, e.g. touch vs vision. Ex: may not completely ignore the left half of space, but instead, may fail to respond to left sided stimuli only under certain conditions such as when fatigued or if simultaneously stimulated bilaterally (e.g. to the left and right half of the face, or the right ear and left hand, etc.), i.e., extinction.

Neglect may also encompass only the left half of an object, even when the entire object falls to the right. Ex: if the word "toothbrush" is presented well to the patient's right, may say seeing only "brush". If presented to her left, may say she sees "nothing".

Not surprisingly, individuals with neglect may also display visual recognition deficits, such as an inability to recognize faces or complex objects. This should not be taken as evidence that the parietal lobe contains facial recognition neurons. Rather, with parietal lesions the ability to search and explore visual, tactile, and even motoric aspects of the environment is disrupted such that only half of a face or tactile stimulus, may be explored. May neglect the left half of images which they consciously conjure up or the left half of words or sentences when reading. This suggests that neglect is for both internal and external events, and greatly involves the ability to internally generate bilateral perceptions.

Neglect also encompasses gravitational influences - receipt and processing information concerning body-positional relationships - via analysis of proproceptive and other forms of input, the parietal lobule also takes into account gravitational influences; the position of the body in space.

Neglect from parietal lesions is probably also secondary to a disconnection of this region from the frontal lobes. That is, the frontal lobes failing to receive input cease to exert activational influences (via its connections with the thalamus, reticular formation) such that information normally processed by the damaged parietal lobe are no longer activated and attended to.

Although not as common nor as severe, inattention and neglect has also been shown to occur following left sided lesions - whereas right hemisphere induced neglect is more profound, attentional disturbances following left cerebral damage tend to be more subtle, e.g. failing to attend to small figures on the right. Or, neglect may only be manifested under procedures employing extinction --when stimulated simultaneously on the right and left halves of the body. Similarly, the right half of drawings, although not neglected per se, may tend to be more distorted and incomplete. Neglect, following left cerebral injuries, however, is more likely to occur with **left anterior rather than left parietal injuries.**
 * LEFT HEMISPHERE NEGLECT**

//Differential Diagnosis / Other factors:// -Sometimes this is due to motoric abnormalities, such as gaze paralysis, or difficulty moving the head or right arm toward the right; i.e. a hypokinesis. -Because of a loss of counterbalancing influences, the right hemisphere acting unopposed also causes such individuals to favor the left half of space. -If verbal report is required, left hemisphere damage is at a disadvantage and what appears to be neglect may in fact be impaired language functioning.

**DELUSIONAL DENIAL** Frequently, patients with **right parietal lesions**, when confronted with their unused or immobile limbs may (at least initially) deny that it belongs to them or swear there is nothing wrong. More often, however, they tend to ignore their left half. In some cases, however, patients may perceive the left half of their body but refer to it using ego-alien language, such as "my little sister", "my better half", "my friend Tommy", "my brother-in-law", "spirits", etc. Some patients may develop a dislike for their left limbs, try to throw them away, become agitated when they are referred to, entertain persecutory delusions regarding them, and even complain of of strange people sleeping in their beds due to their experience of bumping into their left limbs during the night.

It is possible that when the language dominant left hemisphere denies ownership of the left extremity it is in fact telling the truth. That is, the left arm belongs to the right not the left hemisphere. The parietal lobe is in part an evolutionary derivative of the hippocampus (which also contains neurons that code for the position of the body and objects in space), not just a body image and the body in space, but the memory of the body is maintained in this tissue. Memories are sometimes unilaterally stored; i.e. the left hemisphere maintains a somesthetic-memory image of the right half of the body, the right cerebrum maintaining perhaps bilateral representations. In this regard, the left brain may in fact have no memory regarding the left half of the body.
 * DISCONNECTION, CONFABULATION & GAP FILLING**

Inevitably, in order for an individual to confabulate, erroneous information must become integrated in some fashion so that the confabulated response can be expressed.

//Frontal lobe confabulation:// Much flooding of the association and assimilation areas with tangential and irrelevant information much of which is amplified completely out of proportion to more salient details. Consequently, salient and irrelevant, highly arousing and fanciful information are expressed indiscriminately. The normal filtering process is disrupted. //Parietal lobe damage:// rather than flooding, there is a disconnection and information received in the Language Axis is incomplete and riddled with gaps.

Assimilation of input from diverse sources is a major feature of left and right inferior parietal activity. Hence, when this area is damaged errors abound in the assimilation of perceptions and ideas as the language axis can no longer access all necessary information. \When no message is received and when the language axis is not informed that no messages are being transmitted, the language zones instead rely on some other source even when that source provides erroneous input; substitute material is assimilated and expressed and corrections cannot be made (due to loss of input from the relevant knowledge source). The patient begins to confabulate.

In these instances delusions and confabulatory responses occur as a result of an attempt by the Language Axis to fill the gaps in the information received with associations and ideas which are in some manner related to the fragments available and while erroneous, can contain some accurate elements around which erroneous, albeit related, ideations are anchored. Hence, a patient may see his left leg or arm and then state it belongs to the doctor.

//Regions Affected/Involved:// In general, these disturbances occur most frequently when the right frontal or right parietal lobe is damage. However, neglect, denial, and delusional confabulation may also infrequently result from left parietal injuries.

Young children not only produce ego-centric speech, in which they comment upon, explain and describe their own behavior, but sometimes describe their behavior to others (such as their parents) using ego-alien language. They may claim not to know whey they performed certain behaviors, may claim that someone else actually performed the deed for which they are accused, as well as develop imaginary friends with whom they share secrets, play games, or upon whom they may place the blame for some untoward incident. These same "imaginary" friends sometimes urge them to commit certain acts or explain or inform them regarding the actions and motives of others.
 * DELUSIONAL PLAYMATES & EGOCENTRIC SPEECH**

Not all children, of course, develop elaborate imaginary friends. However, all (or almost all) children develop egocentric speech and at times employ ego-alien descriptions when confronted with their own disagreeable behavior.

//Regions Affected/Involved:// Largely, much of this is secondary to corpus callosal immaturity and a reaction of the left hemisphere is response to impulses and behaviors initiated by the right cerebrum and/or limbic system; specifically hyperactivation of the hippocampus and adjoining tissue (which in turn has contributed to the evolution of the parietal lobe). However, among this same age group (up to age 7 and even 10), the parietal lobes are also quite immature, the inferior parietal area in particular.

Following destruction of the inferior parietal lobe and adjoining tissue, patients sometimes uncontrollably comment upon their actions, e.g. "Now I'm waving goodbye", whereas in other instances they may claim that the person performing the action in someone other than themselves. They may in fact completely deny that the left half of their body is their own and claim it belongs to another -which also occurs in some cases of emotional trauma induced injury to hippocampus; a structure which has contributed to the evolution of the parietal lobe. Although a lesioned parietal lobe is not the same as parietal lobe immaturity (particularly in that immaturity is bilateral and damage is usually unilateral), there remains a curious similarity in the behavior of these adults and children, including those who suffer dissociative states secondary to hippocampus-amygdala hyperactivation).

Perhaps this is because the ego and Self is first identified with the body whereas the image of the body is maintained by the parietal lobe. When one parietal lobe (due to damage or immaturity) is unable to communicate with the other half of the brain, the "normal" brain half is unable to recognize a continuity of Self. Consequently, behaviors initiated by the opposite (usually right) half of the brain, or the half of the body controlled by right brain are recognize by the speaking half of the cerebrum only from a disconnected (i.e. alien, dissociated) perspective. When the speaking (i.e. left) hemisphere is questioned about this behavior, or about it's left limbs, they are described as initiated or as belonging to someone else, such as "an old man", "my brother-in-law", or an imaginary friend.