What are the centers for Gaze Movement?

1.Lateral gaze center  is Frontal eyefield (FEF)
Lateral gaze center is Frontal eyefield (FEF) that is situated in area 8 the fibers descend through the internal capsule crosses to opposite side reaches brainstem the para-abducent nucleus of pons through abducent nerve  reaches the  lateral rectus to opposite side.
From para-abducent nucleus  which is the pontine lateral gaze center fibers passes through medial longitudinal fasciculus (MLF) to the  medial rectus nucleus of same side.
Stimulation of FEF result in conjugate gaze to opposite side.
Paralytic or destructive lesion of FEF result in Lateral gaze palsy to opposite side. Both eyes turn to same side.
Frontal eye field also controls saccadic movement to opposite side
Both eye field control vertical saccadic movement. This has regulatory effects on LPS. Stimulation of contraction of LPS resulting in opening of eye and dilatation of pupil.
2.Occipital gaze center area 18-19
Occipital gaze center area 18-19 cortico-fugal fibers passes through the optic radiation - post, limb of internal capsule - cerebral peduncle to 3rd nucleus and MLF.
Occipital gaze center  control the pursuit movement  occipital gaze center of one side control pursuit movement to the opposite side and same side.
Both occipital gaze centers together control vertical pursuit movement
3.Interstitial nucleus of cajal
It is situated at the  level of Superior  Colliculus it control the vertical gaze
4.Central nucleus of perlia is situated  in the mid-brain is the center for convergence
5.Pontine lateral gaze center is close to 6th cranial nerve nuclei, send impulses to ipsilateral  lateral rectus nuclei and contralateral  Medial rectus nuclei through MLF
Stimulation produce lateral gaze to same side
Destruction produce lateral gaze to opposite side.

What is Delusion, Hallucination and Illusion?

Delusion is a false beliefs which cannot be corrected with real facts
Hallucination false perception through a special sense (visual, auditory, olfactory, gustatory) without a stimuli
Illusion is a false interpretation through a special sense with a stimulus.
These are seen in disorders like

• Temporal lobe epilepsy(TLE) – auditory or olfactory hallucination
• Delirium tremens result in visual, tactile hallucination (insect crawling)
• Migraine produce visual aura – scintillating scotoma or teichopsia
• Occipital lobe lesion produce visual aura
• GPI (General Paralysis of Insane) 

Significance of Handedness in neurology

• Handedness is the preference to use the hand of a particular side right or left for complicated, fine and skillful motor acts
• Dominant hand is the hand  that is used for combing the hair , buttoning the shirt or picking up a coin. This is also be tested indirectly by asking the person to kick a ball or to use his or her eye to see through a small hole. 
• The leg or the eye used by the person preferentially, gives a clue to the side of cerebral dominance.
• When the person is  asked to fold his arms across the chest, the dominant arm is placed anteriorly. likewise, when asked  the patient to stand at ease, the dominant hand comes posteriorly.
• There is an anatomic difference in the sizes of dominant and nondominant cerebral hemispheres.
• Planum temporale is an area adjacent to the auditory centre of Heschl's transverse gyrus,it is larger in the left hemisphere in the right handed individuals. Left handedness either hereditary or may due to disease of the left hemisphere in early life.
• Left hemisphere dominance for language occurs in 95% of right handed people. Even in 50% of left handed individuals, left hemisphere is dominant.

Apraxia and its clinical significance

Apraxia is the failure to carry out well organized voluntary movement, despite normal motor, sensory and co-ordination function. So there is a defect in the ability to carry out known acts in the absence of motor weakness, sensory loss or ataxia.
Consequently, the apraxic patient is unable to make use of objects, but their use can be recognized and described. It is tested by asking the patient to use objects I (lighting a cigar, copying a cube, star, duck) or to carry out or imitate certain movements.
Types of apraxia

• Ideomotor apraxia
• Ideational apraxia
• Limb apraxia
• Limb kinetic apraxia
• Buccofacial paraxia
• Dressing apraxia
• Constructional apraxia

Ideomotor apraxia 
In this type of apraxia  automatic movement is normal patient is unable to do it on command, like blowing nose, pushing back hair etc. This refers to the condition where the patient is unable to carry out the motor command, inspite of adequate comprehension of the command and adequate motor and sensory functions to perform the act .It is the most frequent type of apraxia. Here the concept is normal, but execution is defective. In this type of apraxia patient  cannot perform imaginary acts but can do when the real object is given associated with aphasic syndrome—seen in lesion of the dominant parietal lobe
Ideational apraxia 
Carrying out the whole of complex movement is defective,but execution of different parts of movement is normal. This refer to the condition in which patients  is apraxic because they have lost the ideas idea  behind the skilled movements is lost. Here the patient with name and define an object. But do not know how manipulate the object when it is placed in the hand. There is  difficulty in the execution of goal directed sequence of movements. It is  associated with diffuse cortical dysfunction delirium and dementia—due to lesion of bilateral parietal lobes
For example -Lighting a cigarette is not possible.
But its different parts of movement is normal, like taking a match box, holding it correctly and opening it, taking the match, cigarette from cigarette box, etc.
Constructional apraxia
Failure to make design.Patient is unable to draw pictures like star
Koh's block - This is a series of blocks with colors occupying the whole half of one side, persons with constructional apraxia is unable to make the simplest design.
It is due to  lesion of nondoininant parietal lobe
Dressing apraxia 
Patient will put the cloth in the wrong way, unable to start the motion for dressing. lesion of nondominant parietal lobe
Limb kinetic apraxia.
This involves a specific motor disability of one limb. usuallv an arm, in the absence of gross weakness or ataxia. Limb Kinetic Apraxia difficulty in the use of tools seen in focal premotor cortex lesions and corticobasal ganglionic degeneration
Buccofacial apraxia.
The term  refers to the condition in which the patic  cannot perform learned skilled movements of
 mouth, bps, cheeks, tongue and throat in the absence of  motor paralysis ot concerned muscles.
Where is the lesion in Apraxia?
It results from damage to the left parietal cortex or to parietal white matter of the left or of both hemispheres, or from disease of the connections between the two hemispheres through the corpus callosum.
It is a disconnection syndrome
Lesion of dominant supramarginal gyrus –produce bilateral apraxia
Connection problems
Lesion of connection of dominant supramarginal gyrus to the left motor cortex - Right sided apraxia
Lesion of connection of dominant supramarginal gyrus to the right motor cortex through corpus callosum produce -Left sided apraxia
Lesion of non-dominant parietal lobe  result in constructional apraxia.