Parietal & Occipital Lobe Syndromes: Neuropsychological Approach

Neuropsychology is the scientific study of the relationship between brain and behavior. It bridges the disciplines of neurology and cognitive psychology and seeks to describe and explain how cognitions, emotions and behavior are mediated by different processes in brain. In clinical settings, different neurological and psychiatric disorders effect psychological functioning of the patients in terms of information processing, sensory-perceptual processes, attention, execution and other order brain functions. Neuropsychological functioning can be assessed by various sets of neuropsychological batteries available in India. It helps to understand the patients’ neuropsychological deficits and strengths too. The neuropsychological functioning helps in formulating cognitive retraining and holistic management of brain related and psychiaric disorders. The term syndrome entails the group and cluster of symptoms associated with any clinical condition. This paper will briefly focus on the anatomy, functions and various syndromes associated with parietal and occipital lobes and their corrosponding neuropsychological issues.

The brain is splitted into the left and right hemispheres by a bundle of tissues known as corpus callosum. The largest part of the human brain is the cerebral cortex. The very back part of the brain contains the cerebellum (little brain), which is attached to the hindbrain. The Cerebellum has been implicated in the planning and execution of movement and recent work in neuroscience has shown that cerebellum is also involved in cognitive functions (Schmahmann,1997). Midbrain consists of parts known as put amen, substantial nigra, and glob us pallid us. Mid brain is implicated in Parkinson disease and schizophrenia. Forebrain is the largest part of the brain and is broadly involved in intellectual and higher cognitive functions. Each hemi-sphere is divided into four lobes namely, frontal, parietal, occipital and temporal. This paper will focus on the brief anatomy, function and syndromes associated with parietal and occipital lobes.

Neuropsychological Batteries in India
The term battery refers to a group of tests which assesses any specific domains of behavior. In India, the most common neuropsychological batteries used by professional's psychologists are as follows.

Parietal Lobe: Anatomy and Functions
The partietal lobes lie posterior to the central and above the Sylvain fissure postcriorly it is divided from the occipital labe by the imagmary extension of the parieto occipital sulcus on the lateral surface. It is divided into the post central gyrus, the supcrior parictal lobulc, the inferior partictal lobule the supramarginal gvrus and the angular gyrus.
The post central gyrus mediates soma top sensory sensation bodily sensation is represented as a homunculus. A larger cortical surface is devoted to extremetips and the lips. The areas adjoining the post central gyrus from the somatosensory association cortex. Lesions cause abnormal sensations like numbness. Tingling bady image disturbances such as extinction, obscuration or displacement of touch sensation may be present. The displacement can be proximal or distal. It can also be felt outside the body, i.e, exosomesthesia or on the conralateral side (alloesthesia). Touch on two adhacent places may be perceived as one. Two point discrimination is lost when the distane between the two points is perceptible to the normal individual, but not to the parietal labe patient, body image disturbances may be unilateral or bilateral. Unilateral distubances are caused by lesions in the contra lateral parictal labe. Bialteral distubances are caused by lesions in the dominant or left partietal labe. Lesions of the somatosensory cortex and the adjoining association areas can further cause metamorphopsias. These are distortions of body sensations such as feeling of lightness, heaviness, levitation and elongation.
The posterior parietal lobes are adjacent to the occipital lobes. Processing of the visual stimulus continues in the parictal lobe. The paricto occipitall areas are involved in the processing of figure ground relationships. Perception of form, texture, absolute and relative size and distance as well as in the location of objects in visual space. These visuo spatial relations are important for the perception of the total form in a visual stimulus or for the perceptual gestalt. Lesions of the parictos occipital areas cause disturbances of form perception. The perceptual analysis of visual forms in terms of their shape, size, texture or distance is disturbed. Thus perceptual gestalt is also affected. These disturbances are associated with lesions in the non dominant or right parictal lobes.

Constructional Apraxia
Construction of two dimensional or three dimensional forms are disturbed in parictal loba lesion, again more often when the lesions are in the non -dominant partietal lobe. Constructional apraxia for two dimensional figures is present when the patient is unable to copy simple geometrical figures. Distortion rotation micrographia (the drawing is reduced in size) and macrographia (the drawing is enlarged in size) may be present,. Constructional apraxia for three dimensional figures are present when the patient is unable to construct three dimensional forms. The placement of either blocks or sticks even in the simole form of a square may not be possible. In the next stage, if forms are constructed they may be rotated. The form may also be constructed on the design itself, qualifying for the closing in phenomenon, the patient may or may not benefit from cues. Usually constructional apraxia is associated with lesions of the right parictal lobe. If the patient substantially benefits from cues, it can be lateralized to the left partictal lobe. It can be assessed through complex figure and block design tests.

Holme's Syndrome
Disturbances in the perception of absolute distance from oneself to an object is known as absolute localization. The distance between tow objects external to oneself is relative localization. Both these can be disturbed in right parietal lesions. These deficits are manifest when the patient is unable to grasp an object extended to him/her. The reaching movements are not accurate. It appears as if the patient has poor eyesight. Size constancy is lost. The patient perceives the bigger objects as nearer and the smaller objects as father.

Agnosia
Lesions of the left angular gyrus or disonnection of this area from the occipital lobes results in an inability to recognize familial objects through the visual modality. The patient is able to recognize the object through another modality such a touch. This deficit is termed as visual object agnosia. Understanding of a complex scene or a picture may be impaired as in simultagnosia. The patient is able to describe the picture in parts, but is unable to sum up the totality of a scene. Recognitiuon of objects through touch is impaired in parietal lesions, known as tactile agnosia or astereognosis. Familiar objects placed in the hand are not recognised. The deficit may be unilateral wherein the lesion is in the contralateral parietal loba. If it is bilatera, the lesion is in the left p [artietal lobe. Finger agnosia is another condition wherein the patient isunable to name or identify the fingers which are touched. The patient is unable to identify his/ her own fingers and the fingers of the examiner. This is an inability to recognize body parts, is bilateral innature an associated with left partiertal lesions. Anosognosia is an inability to recognize a paralyzed limb as belinging to oneself. Prosopagnosia, the inability to recognize familiar faces visually is associated with right parietal lesions. The patient can recognize the same person through the clothes, vice or the silhouette. Recognition is absent when the faceis seen. The patient may even be unable to recognize his own face in the mirror.
Right parietal lesions are associated with disturbances of visual memory. The localization is to right parietal area when the memory disturbance is for simple visual forms. Memory of places or locations i.e., topographical memory is disturbed in right parietal lesions. The patient is unable to locate familiar places on a map. Independent of the memory deficit, patients with left parietal lesions get lost in familiar surroundings which are termed as route finding difficulty. It can occur even in their own lomes, the patient is able to verbally recall the reut but gets lost while traversing it. The deficit is hypothesized to arise from another parietal deficit which is left-right disorientation. Here the patient gets confused between the left and right sides. Identifying one's left or right side is difficult. The patients are confused when asked to identify the examiner's left or right side.
The left partictal lobe, in particular the angular gyrus is important for writing, reading and calculation, the semantic lexicon is situnted here. lesions cause damage to the lexicon following which comprehension of oral and written language is affected. This condition is the apraxic aphasic alexia. If the arigular gyrus is disconnected from the visuo perceptual centers of the occipital lobe, only alexia is present. It is characterized by impaired reading. Disconnection for the left angular gyrus from the motor engrams situated in the inferior parietal lobule results in agraphia. Writing difficulty or agraphia may be part of visuo perceptual disorders when it is known as spatial agraphia. If the patient is unable to write because of inability to construct two dimensional figures, then it is known as apraxic. Difficulty in calculation or acalculia has two components, spatial acalculia is present when the patient is unable to place numbers properly and is associated with right parictal lesions, difficulty in arithmetic is associated with left parietal lesions. Gerstman's syndrome is associated with left parietal lesions, specifically of the angular gyrus. It consists of acalculia, agraphia, finger agnosia and left-right disorientation.

Unilateral Spatial Neglect
An important sign of right parietal lesions is unilateral spatial neglect or hemi neglect or hemi inattention. Visual attention is not allocated voluntarily to one half of space. The patient is able to attend to it if the attention is drawn to this area verbally. Spontaneously attention is not allocated to the side contra lateral to the lesion. The neglect is usually present on the left half of space. The lesion is in the right parietal lobe. Visual attention is an important function mediated by the right parietal lobe. The right dorsal parietal lobe disengages attention in visual space, if this disengagement does not occur, attention is fixated to one area and other areas are neglected. The attention disengagement results in the patient neglecting all aspects of the contra lateral space. The patient does not see objects on the neglected side and bumps into them. Dressing of one half is neglected. Drawings omit the left half of the figure. Touch is not felt when it is in the left half of the body. Hemi-inattention can occur in right occipital and right frontal lesions also.

Pathology of Emotions
The right parietal lobe is hypothesized to mediate emotions. Normally the right frontal lobe inhibits the right parietal lobe. Lesion of the right frontal lobe removes this inhibitory influence.
Excessive emotions result as in mania or affective disorders. Electroencephalographic (ECG) recordings show the right hemisphere to be more active than the left during emotional stimulation. Dysfunction of the right hemisphere is associated with affective disorders. Studies conducted on stroke patients have indicated that emotional processing is largely lateralized to the right hemisphere. Positive affect is mediated by the left hemisphere. Hence damage to the left hemisphere particularly the left frontal lobe is associated with depression. Negative affect is associated with the right hemisphere. Damage to the right hemisphere reduces the negative affective coning of experience. The result is a disproportionate positive affect resulting in mania. Normal emotions are the outcome of a balanced processing between the two hemispheres.

Sensory Template
Polymodal association cortices of the cerebral cortex are present in the parietal lobes. It is connected to the frontal lobes and to the limbic system. Thus, it is hypothesized that the sensory template of the environment is constructed on a moment to moment basis by the parietal lobe. Its specialization for visuospatial attention spatial cognition as well as the polymodal association area enables it to scan the environment adequately and construct the sensory map. Thus while the frontal lobes are known as the executive centers of the brain the temporal lobes are known as the integrative centers of the brain the parietal lobes construct the sensory template of the world in a dynamic fashion.

Occipital lobe: Anatomy and Functions
The occipital cortex occupies the posterior part of the cerebral cortex. It lies above the cerebellum and is posterior to the parietal and temporal cortices. There are three Brodmann areas in this cortex. The most posterior of these is the area 17 which is also known as the striate cortex. The fibres of the optic tract coming from the eyes terminate here and give it the striate appearance to the naked eye. Area 17 is in the medial portion of the occipital cortex. It consists of simple cells which are sensitive to movement. These cells are also sensitive to specific location and orientation of lines. The cells fire when visual stimuli move. In addition some of these cells fire when the stimuli are in a specific location and orientation. Colour perception also occurs in this area. Area 18 is adjacent to 17 laterally and contains complex cells. Each complex cell receives input from several simple cells. The complex cells are sensitive to orientation. However they are not location specific. They fire across different locations if the orientation is maintained. Complex cell are predominantly present in area 18. Some of these cells receive converging input from both eyes, the remainder receive input only from one eye. The complex cells are probably involved in the earliest stages of actual form perception. Area 19 is adjacent to the area 18 laterally. It contains predominantly hyper complex cells which are sensitive to movement, position and orientation. They process angles, comer, and movements and analyze discontinuity. These cells process geometric forms and it is here that visual closure is present Hyper complex cells together with neurons in the temporal lobe initiate the closure essential to perceive incomplete figures. The faver is most densely represented in the primary visual cortex or the striate cortex. This area also receives input from non visual areas of the brain such as the brain stem nuclei, the pontine arid mesencephalic reticular formation, the lateral amygdala and the lateral hypothalamus. These connections enable the processing of visual stimuli to be influenced by lever of wakefulness and by emotional and motivational influences. The visual cortex is connected to the frontal regions. The association areas of the occipital cortex i.e., areas 18 and 19 arc connected to the inferior temporal lobe and to the parietal lobe. These connections take the processing of visual information beyond the occipital cortex. Visual "stimuli become positioned in space and personally meaningful through these connections.

Occipital Lobe Syndromes
Lesion in the occipital cortex is associated with various disorders of processing visual information. Large and bilateral lesions in the medial calcimine cortex or area 17 lead to cortical blindness. The patient is blind though the eye and retina arc intact. As this area receives maximum input from the fovea patterned vision is lost. The patient is able to discriminate levels of brightness and can make out light from dark. Peripheral vision medicated at the thalamic geniculate level would be present. Consequently though the patient is unable to see they do not bump into large objects. This phenomenon is known as blind sight. Probaly because of this the patient with cortical blindness denies the blindness. If confronted with their blindness they invent reasons and excuses for their disability. This is known as Anton syndrome. If the lesion is partial, the patient might have hemi anopia wherein loss of vision is present in only half of the visual field. Smaller lesions in the occipital lobe lead to hallucinations. Lesions in the area 17 result in hallucinations of moving lights, flashes, sparks and tongues of flame and colours. Objects become exceedingly large which is known as macropsia or exceedingly small which is known as micropsia. Objects also may be elongated or blurred in their outline. Colors might run and objects might lose colour. Lesions in the visual association areas i.e, areas 18 and 19 can produce complex visual hallucinations. These are images of men and animals. Objects and geometrical figures are seen. Micropsia and macropsia can also occur. The objects move towards the patient or recede from the patient. Complex hallucinations are fully formed and are quite real. The patient may not believe that these are hallucinations and might react to them as if they are actually present. Agnosias are the other major disorders occurring in occipital lesions. Visual objects agnosia or the inability to recognise familiar objects through sight is associated with medial occipital lesions, the patient is able to recognize the object though another sensory modality such as touch. Lesions of the left occipital lobe or disconnection of the occipital lobe from the left angular gyrus results in this agnosia. Sometimes, the patient is able to recognise the objects when the object is placed in a familiar context. The patient may be able to draw, pint or trace the object without recognizing it. The object becomes stripped of its meaning. Optic ataxia is present when the object changes its appearance or disappears while the patient is looking at it. Inability to recognise colours or colour agnosia is another condition associated with inferior bilateral occipital lesions. The patient is unable to name, match and identify colour. Prosopagnosia or the inability to recognise familiar face by sight is associated with right occipital lesions. The patient recognizes a face as a face but is unable to place as to whom it belongs. He or she may also recognize the voice without recognizing the face. The lesions are in