Alterations of the occipital lobe in schizophrenia

The occipital lobe and schizophrenia. The anatomical structure

The occipital lobe is popularly known to be associated with the sense of vision. This triangular shaped part of the brain is situated posterior to the parietal lobe. It is delineated on the medial side by the parieto-occipital (PO) sulcus. The lateral side is delineated by an imaginary line that connects the PO sulcus to the pre-occipital notch (known as the parieto-temporal lateral line). The inferior tentorial surface is delineated by a line connecting the pre-occipital notch to the beginning of the PO sulcus, at this point it manifests from the calcarine sulcus. Three Brodmann areas (areas: 17, 18, and 19) are also situated in the occipital lobe. On its medial surface, there is the cuneus, a gyrus localized between the calcarine sulcus and the PO sulcus. The lingual gyrus is present, in the tentorial surface of the occipital lobe (inferior to the calcarine sulcus); this lingual gyrus is separated from the fusiform gyrus by the collateral sulcus. The fusiform gyrus is delineated laterally by the occipitotemporal sulcus.9

Occipital lobe lesions and their neuro psychiatric manifestations. Occipital lobe epilepsy

Occipital epilepsy is not as common as other kinds of epilepsies. It is not commonly known amongst the clinical and non-clinical fraternity, mostly because of its rarity with a prevalence of around 1.2-2.6% cases among the overall cases of epilepsy.10 The hallmark of the occipital seizures are the visual hallucinations, however, they are not present in every case of occipital seizures. Hallucinations usually initiate in the visual field contralateral to the affected visual cortex, and later disseminate to encompass the whole visual field. Transient visual symptoms that may be either the more commonly seen positive symptoms (like phosphenes and flashes) or negative symptoms like (amaurosis, hemianopia, and scotoma) are commonly felt by the patients. Static or mobile flashes, which are the positive symptoms could be considered as the distinctive feature of occipital lobe involvement. The visual hallucinations become colorful and complex, if there is an involvement of the occipito-temporal cortex, with scenes of varying complexity.11,12

Occipital lobe infarction

In comparison with infarctions of other areas of the brain, the occipital lobe infarctions differ in etiology, risk factors, and prognosis.13 Patients with infarctions exclusive to the occipital lobe generally have no other neurological loss besides visual-field loss, and are relatively facile to handle than the patients who have numerous infarctions or have infarctions to other areas of the brain. Visual-field loss from the occipital lobe damage can be managed propitiously and aptly with the optical systems and/or visual rehabilitation. The extent and location of the visual field damage, functional visual needs, and health concerns including personal concerns of the patient are commonly known management factors.14

Dream loss in stroke patients linked to occipital damage

Waknine in 200415 reported that patients with deep bilateral occipital lobe damage complain of total dream loss. This happens in normal sleep (REM). Moreover, the ‘minimal lesion extension,’ which is obligatory for ensuing Charcot-Wilbrand Syndrome (CWS), may be represented by deep bilateral occipital lobe damage with the right inferior lingual gyrus. This study advocated that CWS can depict a discrete and secluded neuropsychological symptom of deep occipital lobe damage, and may occur even in the absence of measurable REM sleep aberrations and other cognitive deficits.

Early visual processing

In the context of social perception, visual social information proceeds through the ventral stream during the early visual processing, and then is sent to regions such as the prefrontal cortex when higher order cognitive processing is necessary. It is reported that face processing transpires in the ventral stream, and position of activation is contingent upon task, indicating a hierarchical arrangement of the ventral stream.16 Categorically, the thalamus may be turned on by the faces, temporo-occipital cortex, fusiform, para cingulate gyrus and lingual gyrus,17 while face and body stimuli also actuate the superior temporal sulcus and middle occipital gyrus.18 The ventral stream may also be linked in the perception of emotional stimuli, via significant connectivity with the amygdala.19 Along these lines, in the ambience of early visual processing, emotional and social information is processed in the ventral stream, in conjunction with the thalamus, temporal, and occipital lobes.

The occipital lobe in schizophrenia

Schizophrenia as already known, consists of delusions, hallucinations, disorganized speech and behavior, and other symptoms, which lead to serious social and occupational problems.20 Presently, here is no lab test to diagnose schizophrenia. However, we believe that the structural MRI and functional MRI could be the future diagnostic modality for the accurate diagnosis of schizophrenia in the 21st century. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, (DSM-V),21 in order to be diagnosed with schizophrenia, the patient must have experienced at least 2 of the following symptoms: delusions, hallucinations, disorganized speech, disorganized or catatonic behavior, negative symptoms. At least one of the symptoms must be the presence of delusions, hallucinations, or disorganized speech. Uninterrupted manifestations of the distress must persist for a minimum of 6 months. During this phase the patient must experience at least one month of active symptoms, with social and/or occupational problems occurring over a notable period of time. These problems, however, must not be attributable to any other condition. Schizophrenia subtypes like residual, catatonic, undifferentiated, and paranoid schizophrenia were removed from the DSM-V by the American Psychiatric Association (APA) because they did not appear to be helpful for providing better treatment or predicting treatment response.22

Structural imaging studies with occipital lobe involvement in schizophrenia

There is enough evidence to support the notion of a reduction in the overall volume of the occipital lobe in schizophrenic patients.23-25 Seven axial MRI sections were used by Zipursky and his team for segmentation.26 They noticed reduction in the volume of gray matter in the occipital lobe in the participating patients. While, another group of scientist reported no group differences between the schizophrenic patients and controls in the occipital lobe.27 Moreover, decreased gray matter in the areas associated with the occipital lobe in schizophrenic patients is also reported in voxel based morphometric studies28 and various other studies.29 There is a lack of extensive previous studies on occipital bone depth. However, later in the 20th century Daniel et al,30 measured occipital bone depth and the occipito median angle in patients with chronic schizophrenia and medical controls. Cranial asymmetry measures among the medical controls and the schizophrenic patients were almost equal. Nonetheless, in right-handed participants with homolateral sighting dominance, a debilitating progression was noticed for more symmetrical tilting along the sagittal suture in the patients suffering from schizophrenia. Cranial asymmetry was able to prophesize increased prefrontal markings in the patients of schizophrenia.30

Phillips et al31 used high-resolution structural and diffusion tensor images and cortical pattern matching methods to juxtapose general and local variations in exterior white matter fractional anisotropy between schizophrenic patients and their relatives, and community comparison subjects and their relatives. Schizophrenic patients showed reduced external white matter fractional anisotropy dispersed crosswise in each hemisphere, especially in the left temporal and bilateral occipital lobes, as compared with control subjects. Additionally, patient relatives, and control subjects, by modeling biological risk for schizophrenia in participants, fractional anisotropy was shown to differ in accordance with relatedness to a patient in both hemispheres and in the occipital and temporal areas. Nevertheless, correction procedures were not survived by the effects, for 2 group comparisons between control subjects and patient relatives.31

A comparison of microstructural diffusion related parameters by whole brain voxel wise map between schizophrenia into its deficit (SZD) and non-deficit (SZND) subtypes indicated that the radial diffusivity was higher in the left forceps minor of SZD patients, in the left internal capsule of SZND patients, and in the right inferior fronto-occipital fasciculus in the whole schizophrenia group. Mean diffusivity was increased from healthy controls to SZD patients to SZND patients in the right occipital lobe.32

Another study revealed that the long duration of untreated psychosis was associated with the temporal and occipitotemporal gray matter volume decrease in treatment naive (treated for the first time) schizophrenia.33 It is also found that the schizophrenic patients have remarkably lower fractional anisotropy in the temporal (superior temporal and parahippocampal) and occipital (superior and middle the occipital) white matter compared with patients with bipolar disorder and healthy volunteers. The temporal and occipital lobe white matter shortfall can also exacerbate the chances of acquiring schizophrenia.34 In some schizophrenic patients, gray matter density increase in the left occipital lobe and basal ganglia exists.35 Fujimoto et al36 studied the imaginary coherence of gamma frequency oscillations with male schizophrenic participants. They found a positive correlation of auditory hallucination and the left occipital and right frontoparietal lobe areas.

In a study involving the first episode schizophrenia patients,37 diffusion tensor imaging (DTI) with voxel-wised analysis of the fractional anisotropy (FA) indicated aberrations in white matter. Cingulum bundle, the left inferior fronto-occipital fasciculus, the left inferior longitudinal fasciculus and the interhemispheric fibers running through the corpus callosum were shown to be involved by fiber tracking.

Wei and his team in 201238 investigated the roles of DTI of white matter at an early stage of the disorder. They found a noteworthy decrease of regional white matter functional anisotropy values in the right anterior and right middle occipital lobe. The study concluded that the decreased white matter in the right anterior cingulated and middle occipital lobe may help in an early diagnosis. It is also reported that the schizophrenic patients with a more serious and debilitating disease possess larger ventricles, smaller prefrontal, temporal and occipital cortices, and smaller subcortical regions.39 The modified white matter solidarity of the left precentral gyrus, cerebellum anterior lobe and occipital lobe could be associated in the neural process of impetuous behaviors in schizophrenia.40 Notable reductions of gray matter are seen in first episode drug naive schizophrenia in bilateral temporal lobe, bilateral occipital lobe, left insula, left frontal lobe superior frontal gyrus, and right lentiform nucleus medial globus pallidus. The unaffected siblings of the same schizophrenic patients, showed remarkable decreases of gray matter especially in the right temporal lobe, bilateral the occipital lobe, and left insula. Studies like these supported the genetic linkage of the mental disorder.41 However, the reduction was mostly evident in the lateral occipital cortex (in the ventral stream) according to another imaging study.42

According to Chan et al,43 first episode schizophrenic patients have lower white matter volume (right temporo-occipital region). Diffusion anisotropy in the right temporo-occipital region disclosed lower planar anisotropy, and higher linear anisotropy (p=0.012) in schizophrenics. Moreover, the facial emotion recognition subtask demonstrated a noteworthy relationship with FA reductions in the left occipital white matter and left posterior callosal area.44

A gradual reduction of gray matter volume in the frontal, temporal, parietal, and occipital lobes of schizophrenic patients was demonstrated. The study suggested that an earlier onset of psychosis especially in schizophrenic patients is associated with an earlier disease related disruption of anatomical brain growth.45 Another important structural imagining study revealed a significant reduction in FA in schizophrenics. This is observed in most major white matter (WM) tracts (corpus callosum, superior and inferior longitudinal fasciculi, inferior fronto-occipital fasciculus, and posterior thalamic radiation).46

Functional occipital lobe abnormalities in schizophrenia (fMRI)

Evidence demonstrates that the population suffering from schizophrenia has decreased activity in the middle occipital gyrus during decision-making assignments. Moderate quality evidence shows decreased functional activity in the right lingual gyrus during episodic memory encoding, and decreased activation of the fusiform gyrus during episodic memory recovery in the patients suffering from schizophrenia as compared with control groups. In addition, moderate quality evidence advocates that schizophrenic patients demonstrate reduced activation during emotion processing tasks in the lentiform, fusiform, and middle occipital gyri. During unequivocal emotional tasks, schizophrenic patients exhibit decreased activation in fusiform gyrus, while implicit emotion was associated with decreased volume in the middle occipital gyri.47-50 Complete brain inspection in patients has also demonstrated subsequent memory activation in the occipital pole, lateral occipital cortex, left inferior temporal gyrus, and fusiform cortex.51

Temporo-occipital and parietal region hyper-activations were also later found by a group of researchers in schizophrenic patients.52 During processing of task-irrelevant aversive pictures relative to neutral pictures, the familial risk group demonstrated less activation of the anterior cingulate cortex, with reduced age related engagement of the inferior prefrontal and occipital parts of the brain. Furthermore, age-related adjustment in enrolment of the frontal, insular, thalamic, and other temporal and occipital parts of the brain could reveal growth changes in the operation of these circuits in people in jeopardy of acquiring schizophrenia.53 Loss in facial emotion recognition is linked with temporo-occipital gray matter volume decrease,54 while in some patients decreased overall occipital activation volume is seen.55

Decreased coupling was most noticeable between fronto-parietal cortical regions and subcortical structures, and between the frontal and occipital regions. Moreover, an increased bond was found among the limbic and frontal zones, and for temporo-occipital coupling.56 While, there have been no variance in temporal, posterior parietal, or occipito-cortex connectivity with the thalamus.57 A study with mapping statistics divulged that the delusion misattribution was linked with thickness in the orbitofrontal cortex (Brodmann’s area [BA] 11/47). On the other hand, delusion, flat affect, and asociality misattribution was associated with cortical thinness in the dorsolateral prefrontal cortex (BA 9/46).58

Hoptman et al,59 studied functional connectivity between homotopic points in the brain using voxel-mirrored homotopic connectivity (VMHC). They performed VMHC research on resting state fMRI data. They found notable reductions in VMHC in patients in the occipital lobe, thalamus, and cerebellum. Early onset schizophrenia patients demonstrate atypical reduction in the connection of the dorsolateral prefrontal cortex with the anterior cingulate cortex, inferior parietal lobule, and middle occipital gyrus.60

Fujimoto T et al61 conducted a research on schizophrenic patients. They collected some images in functional map of event-related desynchronization (ERD) and synchronization (ERS) in theta, lower alpha (8-10 Hz), upper alpha (10-13 Hz), and beta bands. The ERD/ERS changes were noted in the left temporal pole and midline frontal and anterior cingulate cortex in theta ERS, occipital lobe in alpha ERS, and right temporal-frontal-parietal, midline frontal, and anterior cingulate cortex in beta ERD.61 In some other imaging studies, all night sleep data was analyzed by period amplitude analysis. Delta waves during sleep in the bilateral frontal, central, parietal, and occipital areas of the brain were studied. It was observed that the patients had lower total delta wave counts during all-night sleep.62 A psychophysiological interaction analysis of the dorsal anterior cingulate cortex revealed that the activity in the occipital cortex is related to bad social adjustment and impaired social cognition.63 Furthermore, it is also studied that fMRI showed 3 brain networks interrupted in children and adolescents with schizophrenia. These networks included the anterior cingulate and the temporal lobes, cerebellum with subcortical regions, and occipital lobe and the cerebellum. Early-onset schizophrenic patients showed abnormal functional connectivity in the networks involving the temporal lobe, limbic, cerebellum, and early visual processing streams.64

According to a research by Hartberg et al,65 a positive relation was present between the frontal, temporal, and occipital areas and tests for verbal intelligence quotient (IQ), verbal learning, and various executive functions. Diagnostic synergy was observed for the alliance between verbal IQ and the right temporo-occipital junction and left middle occipital gyrus. Another study66 revealed an increase in activation in the left middle and superior occipital lobe. Furthermore, altered prefronto-hippocampal and parieto-occipital connectivity was found to be linked with positive symptoms, which can be helpful in describing the pathophysiology of these symptoms.67

Zhou et al68 indicated that patients suffering from schizophrenia demonstrate remarkably high resting-state functional connectivity density (rsFCD) in the bilateral striatum and hippocampus and significantly lower rsFCD in the right occipital cortex and bilateral sensorimotor cortices. While in another study, Wende et al69 studied that the left inferior frontal gyrus interconnectivity with bilateral occipital cortex is decreased in schizophrenic patients. These kinds of studies could yield primary understanding into the neural correlates of abnormal causal judgements in schizophrenia.69

Metabolic changes involving the occipital lobe in schizophrenia

A systematic review was carried out by Steen et al.70 The whole brain comparison of metabolic N-acetyl aspartate activity (measured by magnetic resonance spectroscopy) in white and gray matter areas in schizophrenia patients versus healthy controls was conducted. Low to moderate quality evidence suggested no differences in N-acetylaspartate (NAA) levels in schizophrenics compared with controls.70 However, another study indicated that the levels of N-acetylaspartate to creatine ratio (NAA/Cr) in the left basal ganglia (p=0.0065) and parieto-occipital lobe (p=0.00498), were remarkably lower in patients with first-episode schizophrenia psychosis than in control subjects.71 Pro-oxidant xanthine oxidase (XO), which is found to play an integral role in purine/adenosine metabolism has decreased activity of XO in the occipital cortex and thalamus of patients with psychosis.72

The results of this comprehensive review indicate that the 82 studies included show that the patients with schizophrenia show structural changes (CT, MRI) in the occipital lobe and some show functional changes (fMRI, PET). On the other hand, some patients show metabolic changes in the occipital lobe (Table 1). Moderate quality evidence (due to large sample size and no consistency and precision) found that the white matter integrity is reduced in the occipital cortex as compared with healthy individuals, moderate to low quality evidence (inconsistent, imprecise) suggests that there is higher frequency of abnormal (reversed) asymmetry in the occipital lobe in schizophrenia as compared with controls. Progressive changes in gray matter volume were reported across longitudinal MRI scans. Significantly greater reductions were reported over time in schizophrenia compared with controls (the occipital gray matter: 69.9%, while the occipital white matter: 45.9%.)

Evidence (moderate quality) also advocates that during executive function tasks, schizophrenic patients demonstrate reduced activity in the middle occipital gyrus. Moderate quality evidence (due to large sample size and inconsistency) suggests reduced activity in the right lingual gyrus during episodic memory encoding, and reduced activation in the fusiform gyrus and right cuneus during episodic memory retrieval in schizophrenia patients compared with controls. Moderate quality evidence suggests that people with schizophrenia show decreased activation during emotion processing tasks in the fusiform, lentiform, and middle occipital gyri. Schizophrenia sufferers showed reduced activation in the fusiform gyrus, while implicit emotion was related with reduction in the middle occipital gyri, during explicit emotional tasks. (Table 2)

Overall results indicated that there was no significant metabolic changes in the brains of the schizophrenic patients. The nature and timing of pathological processes underlying structural, functional, and metabolic changes in schizophrenia remain unclear. Our review provides a selection of studies indicating that the occipital lobe is related to schizophrenia and the occipital lobe abnormalities could be important for schizophrenia and related disorders. Structural brain irregularities in the parietal lobe were found in imaging studies in childhood onset schizophrenia suggesting that gray matter abnormalities commence in the parietal and occipital lobes and continue in a dynamic wave to frontal cortices.73,74 Thus, structural alterations in the occipital lobe may occur early in the course of the illness and point to genetic influences as yet to be determined.75 A study demonstrated that disruptions in neural connectivity in gray and white matter pathways in the occipital lobe are associated with schizophrenia and might indicate a genetic predisposition for the disorder.30 In a post-mortem study of individuals with schizophrenia, Selemon et al76 showed abnormally high neuronal density in the prefrontal and occipital cortices. In the past, neuronal cell death was attributed to be the cause of decreased cortical gray matter volume.77 However, Selemon and Goldman-Rakic78 associated the increased density of cells, in the context of reduced volume, with the loss of neutrophil, or interconnections between the neurons, which could be the result of excessive pruning.

There are studies indicating structural occipital lobe abnormalities in schizophrenia some of them are shown in Table 1. A quantitative MRI study79 suggests that patients with schizophrenia have relative intact gray matter volumes in the primary visual area (PVA), and reduced bilateral volumes of gray matter in visual association areas (VAA), which may be the substrate of some deficits observed in early visual processing. Excessive occipital lobe gray matter loss in several patients is studied,80 moreover a subgroup exists that demonstrates severe perceptual impairments, this shows a primary role for occipital lobe dysfunction in visual stimulus assembly failures in schizophrenic patients.

Evidence regarding functional occipital lobe abnormalities remains unclear as to the direction of the changes in functional activity in the occipital cortex during cognitive tasks in individuals with first episode schizophrenia.34 Another study35 suggests that people with schizophrenia demonstrate reduced activation during emotion processing tasks in the fusiform, lentiform, and middle occipital gyri. During explicit emotional tasks, people with schizophrenia showed decreased activation in the fusiform gyrus, while implicit emotion was associated with decreases in the middle occipital gyri. No measure of consistency or precision in the results was mentioned. According to Ragland et al81 moderate quality evidence (large sample, direct, unable to assess precision or consistency) suggests activity during episodic encoding is reduced in the right lingual gyrus, and reduced in the right cuneus during episodic retrieval in schizophrenia patients compared with controls.

Occipital lobe asymmetries in schizophrenic patients have also been found to be reduced.82 More research is needed to explore occipital lobe functions and volumes across different stages of schizophrenia. More extensive data are necessary from the earliest phase of schizophrenia, to conclude the understanding of the alterations of the occipital lobe in schizophrenia. A better understanding of the time course of structural and functional brain changes will not only help us to differentiate between individuals at risk for schizophrenia and associated mental disorders like psychosis and bipolar disorder, it will further expand our knowledge and understanding regarding the advanced modalities of diagnosis of this severe mental enigma.

In conclusion, with all the above-mentioned studies and results in mind, schizophrenia is associated with the occipital lobe (gray matter and white matter) changes. The volume changes of the occipital lobe are also associated with schizophrenia. The conclusions emerging from this systematic review are useful to initiate new questions and recommendations for further studies, specifically on changes in the occipital lobe in the schizophrenic patient’s brain. The questions like whether the occipital lobe damage (or changes) in schizophrenic patients is confined to just the occipital lobe or does it involve nearby areas. Does involvement of the occipital lobe with nearby areas bring about some related physical symptoms? Or it brings a combination of some psychiatric illnesses with physical symptoms, or if other areas of the brain are also involved besides the occipital lobe, then what is the sequence of the involvement. Therefore, further studies are required to better understand how the progressive brain changes affect the structural, functional, and metabolic activities of the occipital lobe in schizophrenia and the presence of associated physical or psychiatric disorders or symptoms with occipital lobe involvement.