Visual, Visuospatial, and RightBrain Disorders

1
Visual, Visuospatial, and Right-Brain Disorders
2

• Perception refers to the ability to sense a
  stimulus regardless of whether the stimulus is
  recognized. Lesions of the eye or the optic
  nerve produce ipsilateral blindness (partial or
  total) lesions behind the optic chiasm result in
  homonymous visual field defects pathological
  changes in the inferior calcarine cortex produce
  achromatopsia (central color blindness) medial
  occipitotemporal lesions of the right hemisphere
  are associated with prosopagnosia (defective
  recognition of familiar faces) and environmental
  agnosia (impaired recognition of familiar
  places) and bilateral lesions of the medial
  occipitotemporal cortex or inferior longitudinal
  fasciculi cause visual object agnosia.

3
Monocular Blindness
4

• Ocular disorders including diseases of the lens
  (cataracts), retina, or macula produce total or
  partial blindness of the involved eye. Likewise,
  diseases of the optic nerve (such as glaucoma
  affecting the nerve head, ischemic optic
  neuritis, and optic neuritis) produce unilateral
  blindness ipsilateral to the lesion. Pupillary
  responses are usually compromised in diseases of
  the eye and optic nerve because there is
  diminished light conduction, and this sign may
  help distinguish blindness as a manifestation of
  ocular or neurological disease from feigned
  blindness or blindness as a manifestation of a
  conversion reaction.

5

• In addition, patients with conversion disorders
  or who are malingering have intact optokinetic
  nystagmus (nystagmus that is normally induced by
  passing a striped cloth in front of the eyes of a
  sighted person).

6

• Long-standing bilateral blindness may result in
  pendular nystagmus with spontaneous to-and-fro
  movements of the eyes. Visual hallucinations
  (release hallucinations) are not uncommon in
  patients with ocular disorders and may be either
  formed or unformed. Phosphenes (sudden flashes
  of light) often accompany retinal or optic nerve
  disease, and some patients may experience
  synesthesia characterized by phosphenes occurring
  in response to loud sounds or noises.

7
Homonymous Hemianopsia

• Lesions of the optic tract, optic chiasm,
  geniculate nucleus of the thalamus, or the
  geniculocalcarine radiations produce homonymous
  visual-field defects, defective vision or
  blindess in the right or left halves of the
  visual fields of both eyes. Temporal lobe
  lesions are associated with asymmetric
  (incongruent) field defects occipital lesions
  cause symmetric (congruent) defects.

8

• Lesions involving the entire radiation produce
  homonymous hemianopsias (usually with sparing of
  the central few degrees of vision), whereas
  lesions affecting only some of the fiber tracts
  produce quadrantanopsias or other incomplete
  field defects. Pupillary responses are intact in
  patients with homonymous visual-field defects,
  and visual acuity is normal.

9

• Hallucinations are common in the period
  immediately after an injury to the
  geniculocalcarine radiations (e.g. in the first
  few days after a stroke) and may be unformed
  (lights), semiformed (tire track or herringbone
  patterns), or formed (complex scenes, animals, or
  people). The hallucinations are commonly
  confined to the area of the visual-field defect.

10
Achromatopsia

• Achromatopsia refers to central color blindness.
  The patient loses the ability to distinguish
  color in the contralateral visual field. The
  associated lesions involve the cortex inferior to
  the calcarine fissure of the medial occipital
  lobe. There is often an associated partial
  hemianopsia. The color blindness is difficult to
  demonstrate except when it is bilateral. Color
  blindness is assessed with color-naming tests,
  tests requiring sorting of colors by shades, and
  Ishihara pseudoisochromatic plates.

11
Simultanagnosia

• Agnosias are recognition deficits rather than
  perceptual disturbances. Simultanagnosia is a
  misnamed exception. In this disorder, when the
  patients are shown two objects simultaneously,
  they fail to perceive one of them. For example,
  when shown a figure consisting of a circle and a
  cross, they see the circle or the cross but not
  both when shown a number drawn by juxtaposing
  many small numbers (for example the number 2
  drawn by using many little number 3s), they see
  the number 2 or the number 3s but not both.

12

• Simultanagnosia is often observed as part of
  Balints syndrome. The latter consists of optic
  ataxia (the inability to touch objects accurately
  using visual guidance), sticky fixation or
  occular apraxia (difficulty volitionally
  redirecting gaze), and simultanagnosia.

13
Prosopagnosia

• Prosopagnosia refers to the inability to
  recognize familiar faces. Visual perception is
  intact the patient sees normally and can
  describe the unrecognized face in detail.
  However, familiar faces, such as the faces of
  family members and famous people, cannot be
  recognized, and the patient cannot deduce the
  individuals identity without the aid of
  nonvisual clues. In some cases, specific facial
  features (moustache, glasses of a specific type)
  are used to facilitate recognition, but the
  patient is easily fooled if someone with similar
  characteristics appears.

14
Environmental Agnosia

• Environmental agnosia is a clinical syndrome
  characterized by the inability to recognize
  familiar places. The patient sees normally and
  is able to describe the surroundings but has no
  sense of familiarity. Patients commonly adopt
  verbal strategies to compensate for the deficit
  for example, they may find their homes by using
  the street signs and house numbers.
  Environmental agnosia and prosopagnosia
  frequently coexist.

15
Visual Object Agnosia

• Two principal types of visual agnosia have been
  identified apperceptive agnosia and associative
  agnosia. The two identified syndromes reflect
  disruption of different stages of processing of
  complex visual information, and variations of the
  syndromes are common. Apperceptive visual
  agnosia is characterized by intact visual acuity
  but an inability to recognize objects.

16

• Patients can distinguish shades of light
  intensity, identify colors, determine line
  orientation, exhibit depth perception, see
  movement, and distinguish thin from thick lines.
  They can negotiate their surroundings but cannot
  recognize, describe, or match perceived objects.
  They cannot draw objects they see and cannot
  point to objects named by the examiner. The
  agnosia involves all visual stimuli including
  faces, the environment, and objects.
  Apperceptive agnosia may occur as a phase of
  recovery from cortical blindness after anoxia,
  carbon monoxide poisoning, or bilateral posterior
  hemispheric strokes.

17
Apperceptive visual agnosia is a failure in
higher level perception, also known as
visual-form agnosia. ?The person has normal
visual acuity, but cannot recognize objects based
on their shape. The person cannot recognize
objects, line drawings of objects, nor copy
drawings of objects. They do not know what they
are seeing. A person here could describe a rose
in intimate detail but not know it was a rose
until smelling it. ?Prosopagnosia is a form of
apperceptive visual agnosia in which the person
cannot recognize a face visually, but can do when
hearing their voice. Here, some individuals do
not recognize their own face.
18

• Associative visual agnosia features intact
  elementary perception and preserved ability to
  describe, draw, and match visual stimuli. For
  example, when shown an object (shoe, toothbrush,
  etc.), patients can draw the object and match the
  object with an identical one from a group of
  objects, but they cannot recognize the object or
  describe its use.

19
?Associative visual agnosia refers to a
disconnection between perceptions and verbal
systems. The person cannot verbally label or name
what they see but they can label or identify it
nonverbally by gesture or behavior which
correctly discriminates the object. A person
here could not say an object was a car or not but
they could make gestures of using a steering
wheel to indicate they can correctly discriminate
the object but it cannot be verbally labeled. A
person here could copy a drawing of an object but
not name it but they could not produce a drawing
of an object if merely asked. A drawing of a car
could be reproduced but the person could not do
so in response to Draw a car.
20
Color Agnosia

• Color agnosia (also called color anomia) is
  present in some patients who have alexia
  (inability to read) without agraphia (inability
  to write). The patients do not have
  abnormalities of color naming and can name the
  colors appropriate to specific settings (a banana
  is yellow, a fire engine is red) they also can
  sort and match colors. They do not have color
  blindness. They cannot point to named colors or
  name colors pointed to by the examiner.

21
Disturbances of Visuospatial Attention
22
Unilateral Neglect

• Unilateral (or hemispatial) neglect refers to a
  lack of attention to events and actions in
  one-half of space. Neglect may involve all
  sensory modalities visual, auditory, and
  somatosensory as well as motor acts (motor
  neglect in-intention) and motivation.
  Unilateral visual neglect is the most commonly
  observed form of hemispatial neglect. In its
  most subtle form, the patient ignores the
  stimulus presented in the neglected hemifield.

23

• This type of neglect can be demonstrated by
  holding one hand in equivalent portions of each
  visual field while facing the patient, quickly
  moving the fingers of each hand, and asking the
  patient to point to the hand whose fingers moved
  (the technique of double simultaneous
  stimulation). The patient will perceive movement
  only in the non-neglected visual field (this test
  requires that the patient not have a field
  defect).

24

• In its more obvious form, unilateral visual
  neglect may be evidenced by failure to copy
  one-half of model objects, read one-half of
  words, dress one-half of the body, or shave
  one-half of the face. Tests for visual neglect
  include line bisection (the patient crosses the
  line in the middle of the nonneglected portion)
  and the line-crossing test, in which the patient
  is given a sheet of paper with randomly
  distributed lines and is asked to cross each line
  in the middle only those lines in the
  nonneglected field will be crossed.

25

• In severe forms of neglect, all types of stimuli
  in the affected hemiuniverse are neglected.
  Somesthetic neglect is demonstrated by touching
  the patient simultaneously on both sides of the
  body and asking the patient where he or she was
  touched the patient perceives only the touch on
  the nonneglected side of the body.

26

• Auditory neglect is assessed by standing behind
  the patient, snapping the fingers on either or
  both sides of the head, and asking the patient to
  point toward the side where a stimulus was heard.
  The patient points only toward the nonneglected
  side during double simultaneous auditory
  stimulation.

27

• Motor neglect syndromes involve action-intention
  disorders affecting the half of space
  contralateral to frontal lobe or basal ganglia
  lesions. The patient may appear to have a
  hemiparesis because the limb with
  action-intention neglect is unused, but when
  strength and coordination are tested, they are
  found to be normal.

28
Anosognosia and Anosognosic Syndromes

• Anosognosia is the clinical syndrome
  characterized by denial of hemiparesis. It
  classically occurs in patients with right
  parietal lesions and left unilateral neglect who
  deny their left hemiparesis. Variants of
  anosognosia include somatoparaphrenia (denial of
  ownership of the paralyzed limbs), anosodiaphoria
  (minimization of and unconcern about the weakness
  without complete denial), misoplegia (hatred of
  the paralyzed or weak limb), personification
  (naming the limb and giving it an identity), and
  supernumerary limbs (reduplication of limbs on
  the neglected side).

29
Visual Anosognosia
30

• Also called Antons syndrome, visual agnosia
  (from the Greek, a negation nosos
  disease gnosis knowledge) is the denial
  of blindness in patients who have irrefutably
  lost their vision. Whether they walk into the
  walls under their own stream or are bluntly
  confronted with their disability by you or
  others, their response is indifference, am
  implausible explanation (e.g., I lost my
  glasses), or both.

31

• Antons syndrome is distinct from phantom vision,
  in which enucleated patients or those with
  severed optic nerves claim to perceive light and
  shape. The existence of visual subception
  suggests two dissociable levels of seeing,
  instrumental behavioral responses to optical
  stimuli on the one hand, and subjective visual
  awareness on the other. These patients do not
  readily volunteer their experiences of seeing
  things. In fact, they feel ashamed at
  experiencing something that intellectually they
  know to be not real.

32

• For example, after fifty-year-old patient ER had
  her left eye enucleated because of a melanoma,
  she began to see geometric figures in that eye.
  The shapes were external, close to the face, and
  consisted of metabolic blobs, spirals, and
  parallel lines. Her explanation was, This is
  involuntary. My brain is doing it. (This claim
  is most plausible. We have long known that
  migraineurs who have no eyes nonetheless have
  visual symptoms during their aura.

33

• The inverse of Antons syndrome has also been
  reported namely, the denial of visual
  perception in a man with remarkably preserved
  visual skills in his upper right quadrant. When
  confronted with his success in correctly
  identifying colors, objects, faces, facial
  emotions, and words, he denied any awareness of
  visual perception. His explanation for his
  accurate performance was, I feel it.

34
Visual Illusions and Hallucinations
35

• Visual illusions and hallucinations may be either
  positive or negative symptoms and can be seen in
  drug reactions or withdrawal, delirium, epilepsy,
  and mass lesions. They may be elementary or
  formed. Epileptic discharges in Brodmann areas
  18 and 19 (visual association cortex) (lateral
  occipital) are said to cause twinkling or
  pulsating lights. Striate lesions produce
  elementary visual sensations of dark shapes,
  phosphenes, and flashes that may be stationary or
  moving, colored or achromatic. Red is perceived
  most often, followed by blue, green, and yellow.
  These visions may appear straight ahead or in the
  visual field opposite the legion.

36

• Elementary flashes of light, zigzags, or other
  geometric shapes are called photisms, and are
  distinct from phosphenes, the flashing lights one
  sees on firmly rubbing the eyes. Phosphenes are
  caused by mechanical deformation of the retina
  and are an example of an entopic perception
  (literally within the eye). These latter need
  to be distinguished from perceptions of cerebral
  origin as the eye and the occiput are poles apart.

37

• Other entopic phenomena are the seeing of ones
  own retinal blood vessels, vitreous floaters,
  afterimages, or the muscae volitantes. Entopic
  perceptions appear to move with the eyes, whereas
  perceptions of cerebral origin are independent of
  eye movement. Afterimages are produced by
  fatigued retinal photoreceptors and are
  complimentarily colored images of cerebral
  origin are often chromatic. Retinal vessels and
  floaters look like cobwebs or blobs, are fixed in
  appearance, and can be viewed or ignored at will.
  The muscae volitantes are the actual corpuscles
  coursing through vessels near the macula. You
  should normally be able to see your own,
  particularly against a bright sky or a field of
  snow.

38

• They travel in lines or arcs, then disappear.
  Awareness of your own normal retinal circulation
  is called Scheerers phenomenon. Traction of the
  vitreous or retina causes arch-shaped, achromatic
  phosphenes called Moores lightning streaks.
  Macular edema or hemorrhage will produce
  distortions such as heat waves, and glaucoma
  causes halos and rainbows around objects.
  Certain maculopathies can also cause
  metamorphopsia.

39

• Release hallucinations are perceptions, in any
  modality, that occur in a deafferented field.
  Visual and auditory ones are most common.
• Visual release hallucinations can wander out into
  the normal field. They are experienced in
  extrapersonal space, and patients almost always
  appreciate their unreal nature. Elementary
  hallucinations tend to occur with occipital
  lesions, whereas formed and more complex ones
  emanate from the temporal lobe. Hallucinations
  due to temporal lobe lesions tend to fill both
  visual fields, in contrast to those engendered by
  occipital lesions, which usually inhabit only the
  contralateral field.

40

• Elementary visual hallucinations have many
  causes, and the ground is strewn with confounds.
  In addition to entopic and occipital lobe causes,
  hallucinations can also result from lesions of
  the anterior optic tract. These are special,
  however, in that they are not spontaneous but
  rather are induced by another sense, most often
  sound. This is an example of an acquired
  synesthesia. Sounds that induced photisms in
  these patients included clanking of the radiator,
  crackling of the walls as they cooled at night,
  the whoosh of a furnace ignition, a dogs bark,
  and slamming doors.

41

• The photisms ranged from simple flashes of white
  light to colored forms that looked like a flame,
  amoebas, oscillating flower petals, a spray of
  bright dots, or kaleidoscopic effects. All
  lasted for just an instant. The monocular
  visual-evoked response from the scotomatous eyes
  showed conduction delays and reduced amplitudes.
  It is curious that photisms arising in one eye
  are perceived to be caused by sounds reaching
  only the ipsilateral ear. This is, of course,
  contrary to our conventional understanding as
  acoustic localization depends on differences in
  the sound reaching both ears.

42
Metamorphopsia and Allied Experiences
43

• Many bizarre visual experiences are subsumed
  under the term metamorphosia, the essential
  features of which are (1) deformation of shape,
  (2) change in size, (3) the illusion of movement,
  or (4) all three. Its locus is imprecise, being
  vaguely in the occipitotemporo-parietal territory.

44

• In metamorphopsia, objects may appear to advance
  or recede relative to the viewer, their vertical
  or horizontal orientation may suddenly skew, or
  objects may break apart as if they were painted
  on glass, the parts sliding over one another as
  in Cubism. One object may transform into
  another, sometimes with the two shapes
  alternating rhythmically back and forth. Visual
  field defects are frequently found in all these
  subjective visual experiences. Specific types of
  metamorphopsiae have earned their individual
  terminology.

45

• In micropsia and macropsia, objects seem too
  small or too big, respectively.
• Umkehrtsehen is German for inverted vision,
  meaning that things look as if you are standing
  on your head. Verkehrtsehen denotes the reversal
  of right and left. These aberrations usually
  appear and resolve suddenly, and the experience
  is transitory in all recorded cases.

46

• Palinopia (also known as paliopsia, paliopia, and
  palinopsia) is visual preservation. For example,
  a patient saw his wife leave the hospital room,
  and then he saw her leave again a few moments
  later. Aside from static cerebral lesions,
  antiserotonergics such as LSD and mescaline can
  produce it. LSD users speak of trails,
  positive images that remain immediately behind an
  object as it moves across their visual field.

47

• Polyopia signifies multiple images of the same
  object. For example, a patient looked at a
  single rose and, on turning away to look at the
  blank wall, saw multiple roses. Insect vision,
  or entomopia (from the Greek entomon meaning
  insect), connotes rows and columns of multiple
  images numbering in the hundreds, as might be
  experienced by looking through compound eyes.
  Polyopia is a form of cerebral diplopia.

48

• Cerebral diplopia (double vision) may be vertical
  or concentric. Strict terminology would limit it
  to only two images (the above terms of polyopia
  and entomopia taking care of larger iterations),
  yet triple impressions are especially common.
  Migraine is probably the most common cause of
  cerebral diplopia.

49

• Monochromatopsia refers to illusory coloration,
  such as erythropsia (red) or xanthopsia (yellow).
  Vitreous hemorrhage causes the former and
  digitalis intoxication the latter more often than
  do cerebral lesions.

50

• The term achromatopsia, indicating no color
  seeing, is somewhat misleading because patients
  do perceive some color. The chroma that they see
  is pale and desaturated, however, as in a
  television whose color is turned down. Patients
  also describe a spatial gap between the
  normally saturated field and the achromatic one.
  The responsible lesion is in unimodal visual
  association cortex.

51
Auditory Illusions and Hallucinations
52

• The term paracusia refers to an alteration of
  volume, timbre, or some other distortion of
  sound. This may be both unpleasant and
  persistent. Unlike tinnitus and other auditory
  perceptions caused by end-organ disease,
  paracusiae are cerebral in origin. This is
  analogous to the distinction between entopic and
  cerebrally based visual hallucinations. Auditory
  hallucinations may be elementary or complex,
  ranging from humming and buzzing to music,
  voices, and radio programs.

53

• Their cause is not limited to the temporal lobe,
  however. Ipsilateral musical hallucinations, for
  example, also result from lesions in the pontine
  tegmentum. That such brainstem hallucinations
  usually occur in the context of hearing loss
  suggests that they may be an instance of release
  hallucinations.

54
Olfactory and Gustatory Hallucinations
55

• Olfactory hallucinations are customarily
  associated with mass lesions or epileptic
  discharges in the inferior and medial segments of
  the temporal lobe, especially the hippocampal
  convolution or uncus hence the name uncinate
  fits when referring to the disagreeable smell
  that sometimes constitutes the aura of partial
  seizures. It is externally projected and
  experienced as coming from some nearby but
  unknown source. The smell is impossible to
  identify other than being described as foul,
  rancid, or vile. (This quality of
  indescribableness is characteristic of experience
  associated with temporal structures.

56

• Gustatory hallucinations also arise from the
  temporal lobe. Intense and sudden hunger can be
  a symptom of temporal lobe epilepsy (TLE), and,
  paradoxically, also of lobectomy. A boy was
  reported to have experienced two episodes of
  right anterior temporal intracerebral hemorrhage,
  each preceded by exclamations of intense hunger.

57
Synesthesia
58

• The term synesthesia derives from the Greek syn
  (meaning union) and aisthesis (sensation),
  and refers to an involuntary joining of one or
  more senses. That is, perception in one sense is
  accompanied by a parallel perception in another
  sense. Synesthesias medical and psychological
  history reach back 300 years.
• Idiopathic synesthesia is not a disorder per se,
  but a perceptual curiosity found in roughly 1 in
  25,000 individuals. Women outnumber men by at
  least two to one, and left-handedness or mixed
  dominance is more common than expected.

59

• Through permutations of the five senses yield
  twenty possible pair-wise combinations, some
  synesthetic combinations are much more common
  than others. The yoking of sight with sound is
  by far most frequent, touch and taste less so,
  and smell is least often involved. In colored
  hearing synesthesia (chromesthesia), words,
  voices, environmental sounds, or music will
  trigger the perception of an involuntary photism
  that is perceived in extrapersonal space. In a
  case that I called geometric taste (i.e.,
  taste-touch synesthesia) the taste of mint caused
  subject MW to palpate a cold, smooth, curved
  shaped in front of him.

60

• We often emphasize the yoking of just two senses
  when speaking of idiopathic synesthesia, though
  polymodal synesthesia occurs as well.
  Individuals mention that a third or fourth sense
  sometimes participates, but not as often as the
  main two that are joined. It is important to
  distinguish that synesthetic percepts are neither
  metaphoric nor pictorial. They are concrete,
  generic, and unelaborated. By generic, it is
  meant that synesthetes see blobs, lines, spirals,
  and lattice shapes palpate smooth or rough
  textures agreeable or disagreeable taste
  flavors, such as salty, sweet, or metallic.

61

• They do not see pastures and temples, taste
  chicken soup, or feel a sponge or some other
  specified object. Sensations never go beyond
  this elementary, unembroidered level to become
  specific exemplars.
• Acquired synesthesia is classically seen in TLE,
  head trauma, and mass lesions involving the
  medial temporal lobe. Synesthesia may also be
  induced by sensory deprivation, antiserotonergic
  hallucinogens such as LSD and peyote, or direct
  electrical stimulation of subcortical limbic
  structures.

62
Other Subjective Experiences Dependent on the
Temporal Lobe
63

• Extremely unusual subjective perceptions have
  been recorded in cases of TLE and in patients
  with other known temporal lobe pathology.
• Time dilation or time contraction occurs with
  lesions of either temporal lobe. Changes in the
  perception of time are certainly cognitive and,
  because they emerge following temporal-lesions
  one would expect to find them associated with
  other interesting neurological conditions.

64

• Déjà vu and deja vecu mean already seen and
  already experienced (the latter literally means
  already lived), and refer to ones sense that
  something novel is extremely familiar or has been
  experienced exactly so at some past time. Jamais
  vu and jamais vecu refer to the opposite sense
  that a familiar setting feels nonetheless alien
  and strange.

65

• The feeling of presence is not an uncommon
  experience, yet its occurrence rarely is
  volunteered for fear of negative judgment.
  Sensing a presence can occur in pathological
  states as well as be part of normal experience
  in the latter case, it is most often experienced
  late at night or at times of great creativity.

66

• Other odd personality characteristics that are
  said to be typical of those who suffer from
  temporal lobe seizures are a heightened interest
  in religion and cosmic matters, the keeping of
  diaries or voluminous writings, a sense of
  portentousness or the attribution of heightened
  significance to otherwise mundane events, and a
  viscous or sticky personality.

67
Cortical Sensory Disturbances
68

• Where we once were content to call the single
  post-central gyrus the somatosensory cortex, we
  now know that five somatosensory cortical areas
  exist in humans, each with its distinct
  somatotopic representation, cytoarchitecture, and
  projections.

69

• Knowing what relative roles the various
  somesthetic cortices play in human sensation is
  another matter. At present, we can say that
  dorsomedial lesions produce severe anesthesia and
  apraxia that eventually improve considerably.
  Ventrolateral lesions, in contrast, produce
  tactile agnosia that remains detectable years
  after brain injury.

70

• Pain, though less well understood than other
  sensory systems, also has multiple cortical
  representations. Painful heat, for example,
  activates contralateral anterior cingulum, S1,
  and S2, a pattern distinct from the predominant
  S1 activation caused by vibrotactile stimulation.
  Because the forebrain usually is thought to
  regulate emotion, the specific cingulate
  representation of pain is unexpected.

71

• Categorization of sensory loss on clinical
  grounds is far less confusing. Patients with
  loss of one or more elementary sensations (touch,
  pain, temperature, vibration) in a
  face-arm-leg-trunk pattern have inferior-anterior
  parietal lesions involving the parietal operculum
  and insula. Theirs is a pseudothalamic sensory
  syndrome in that it mimics a lesion of lemniscal
  or spinothalamic projections. Other individuals
  who lose the ability to discriminate sensation
  (stereognosis, graphesthesia, proprioception)
  have superior-posterior parietal lesions. Theirs
  is called a cortical sensory syndrome.

72

• A somatic hallucination that bears a superficial
  resemblance to release hallucinations is
  alloesthesia, a condition in which a noxious
  sensory stimulus given on one side of the body
  (where a sensory deficit exists) is perceived at
  the corresponding locus on the opposite side.
  This aberration occurs with lesions in the
  putamen and spinal cord, represents an elementary
  disturbance of sensory pathways, and is not to be
  mistaken for a higher cortical dysfunction.
  Segmental sensation or pain can also be referred
  to a different and quite distant dermatome via
  spinal mechanisms.

73
Asomatognosia
74

• Asomatognosia is a disturbance of
  awareness/knowledge about ones own body and
  bodily conditions, the perception of ones own
  physical self, the relations of its parts to the
  whole, and its orientation and extension into
  extrapersonal space. One form would be asymbolia
  for pain in which normal reactions to painful
  stimuli are not evidenced or autotopagnosia, the
  inability to localize, name, or orient correctly
  different body parts

75
Asomatognosia/Autotopagnosia

• Fails to point to correct body part upon command
• Fails to correctly imitate body positions,
  postures or movements
• Fails to correctly name body parts