Simultanagnosia

Key points at a glance

Key Points of This Disease

• A higher-order visual disorder in which individual objects can be recognized but the overall scene cannot be grasped.
• Most commonly caused by bilateral parieto-occipital lobe damage, classified into dorsal and ventral types.
• One of the components of Balint syndrome (optic ataxia + oculomotor apraxia + simultanagnosia).
• Occurs due to various etiologies such as cerebrovascular disease, Alzheimer’s disease, and posterior cortical atrophy.
• Visual acuity and ocular structures are often normal, and patients may present to ophthalmology with vague visual complaints.
• If a person cannot read numbers on the Ishihara color vision test despite having normal color vision, it is useful as a screening for simultanagnosia.
• There is no fundamental drug therapy; treatment focuses on the underlying disease and rehabilitation.

1. What is simultanagnosia?

Simultanagnosia is a condition in which individual elements can be recognized, but multiple stimuli cannot be perceived simultaneously and interpreted as a whole. The classic phrase “cannot see the forest for the trees” is used.

History and definition

In 1909, Rezső Bálint reported psychic paralysis of gaze, optic ataxia, and spatial attention disorder. In 1924, Wolpert named it “simultanagnosia.”

Classification

Dorsal type

Lesion site: Bilateral parieto-occipital lobes

Features: Primarily spatial inattention. This type is seen in Balint syndrome, where multiple objects cannot be recognized in the same scene. Collides with objects while moving.

Ventral type

Lesion site: Occipitotemporal lobe

Features: Impaired parallel perception of multiple objects and overall picture comprehension. Compared to the dorsal type, collisions with objects are less frequent. ¹⁾

Relationship with Balint syndrome

Balint syndrome is defined by the triad of optic ataxia, oculomotor apraxia, and simultanagnosia. Simultanagnosia is one component but can occur alone. Extensive damage to the dorsolateral pathway underlies Balint syndrome.

• Optic ataxia and oculomotor apraxia: Caused by disruption of connections from V1 to the frontal eye fields.
• Simultanagnosia: Caused by disruption of connections to the dorsal parietal lobe.

Balint syndrome occurs in watershed infarction and visual Alzheimer disease. If acquired oculomotor apraxia is accompanied by optic ataxia and simultanagnosia, a diagnosis of Balint syndrome is made.

Epidemiology

There are no epidemiological data for simultanagnosia as a standalone disease; it depends on the underlying condition. It can appear as an initial symptom in neurodegenerative diseases (Alzheimer’s disease, posterior cortical atrophy). ¹⁾

Q How is Balint's syndrome different from simultanagnosia?

A

Balint’s syndrome refers to the triad of simultanagnosia, optic ataxia, and oculomotor apraxia. Simultanagnosia is one component and can occur alone. Balint’s syndrome generally involves more extensive brain damage than simultanagnosia alone.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

• Difficulty recognizing multiple objects: In complex visual scenes, unable to recognize multiple elements simultaneously.
• Colliding with objects: Frequently bumps into objects or walls.
• Depth perception problems: Cannot accurately judge distances.
• Difficulty reading: Can only recognize one letter at a time (letter-by-letter reading). ¹⁾
• Vague visual complaints: May present with vague complaints such as “vision is not clear.”
• Normal visual acuity: Visual acuity (20/20 equivalent) is often preserved.
• Visual field defect: May be accompanied by homonymous hemianopia.
• Range of severity: Varies from mild to severe, interfering with daily life.

Clinical Findings

• Abnormality on Ishihara color test: Despite normal color vision, the patient cannot integrate individual color dots as a whole and thus cannot read the numbers on the plates.
• Difficulty understanding complex visual scenes: Unable to grasp the overall scenario in the Boston Cookie Theft picture or the Telegraph Boy, identifying only individual components.
• Ophthalmic findings are usually normal: Visual acuity, anterior segment, and fundus examinations are often normal.
• Points to note in visual field testing: Fixation may be poor, making visual field measurement difficult. Even if quantitative perimetry is normal, simultaneous agnosia may be detected by confrontation testing.
• Differential diagnosis of ventral type: The scattered dot counting test is useful. However, it cannot be applied if hemispatial neglect is present. Having the patient point to objects in the room as instructed suggests ventral type (simultanagnosia for pictures only). ¹⁾
• When Balint syndrome is comorbid: It is accompanied by optic ataxia (knowing where an object is but unable to reach and grasp it) and oculomotor apraxia (inability to voluntarily move the gaze).
• Characteristics of higher visual dysfunction: Patients’ complaints are often vague, and it is important to perform tests specific to the symptoms predicted from the lesion location.

Q Why is vision poor even though visual acuity is normal?

A

Even if the eye structure and visual acuity itself are normal, higher-order visual cognition (the ability to perceive multiple objects simultaneously and integrate them as a whole) is impaired, making it difficult to grasp the overall visual scene. This is not an ophthalmological problem but a problem of the higher visual cortex of the brain.

3. Causes and Risk Factors

Cerebrovascular disease is the most common cause overall. Occipital lobe damage is often due to posterior cerebral artery (PCA) infarction. Since the parieto-occipital lobe is a watershed area between the middle cerebral artery and the posterior cerebral artery, cerebral hypoperfusion is a major cause in the acute phase.

Cerebrovascular Disease

Watershed infarction: Most common cause in the acute phase. The parieto-occipital lobe is vulnerable.

Posterior cerebral artery infarction: Major cause of occipital lobe lesions.

Cerebral hemorrhage: Direct damage to the parieto-occipital lobe.

Neurodegenerative Diseases

Alzheimer’s disease: May present as visual Alzheimer’s disease.

Posterior cortical atrophy (PCA): Onset around age 60. Main symptoms are visuospatial and perceptual deficits. The most common cause is AD (Alzheimer’s disease). There are dorsal (parieto-occipital) and ventral (occipitotemporal) subtypes. ¹⁾

Other Etiologies

Infiltrative tumors: Local infiltration into the parieto-occipital lobe.

Traumatic brain injury: Parieto-occipital lobe damage due to high-energy trauma.

Demyelination/Infection: Multiple sclerosis, encephalitis, etc.

Lesion location: Bilateral parieto-occipital lobes are most common. Rarely, it can also occur with right unilateral parieto-occipital lobe, bilateral occipital lobe, or unilateral parietal lobe damage.

Risk factors: Hypertension, diabetes, dyslipidemia (as risk factors for cerebrovascular disease), trauma, and associated risk factors for neurodegenerative diseases.

Prevention and Daily Care

Prevention of simultanagnosia primarily involves managing the underlying disease. To prevent cerebral infarction, properly control hypertension, diabetes, and dyslipidemia. For prevention of recurrence after cerebral infarction, it is important to continue antiplatelet or anticoagulant medications as directed by your physician.

4. Diagnosis and Examination Methods

There are no formal diagnostic criteria. Diagnosis is made by combining clinical findings and neuroimaging.

Clinical Evaluation

• Complex visual scenes: Present complex scenes such as the Boston Cookie Theft picture or the Telegraph Boy and ask the patient to describe the overall scenario. Patients with simultanagnosia cannot grasp the entire scene and only list individual elements.
• Ishihara color vision test: Color vision is normal, but the patient cannot read the numbers on the plates because they cannot integrate individual color dots. Useful for screening in ophthalmology.
• Navon figure test: Present stimuli consisting of small letters that form a large letter. Patients with simultanagnosia can recognize the small letters but cannot recognize the large letter they form. ¹⁾
• Confrontation test: Even if quantitative perimetry is normal, simultanagnosia may be detected by confrontation testing. In higher-order visual dysfunction, patient complaints are vague, so it is important to perform tests specific to symptoms predicted from the lesion location.

Neuroimaging

The main uses of each test are shown below.

Test	Main use
MRI (first choice)	Evaluation of tumors, infarction, hemorrhage, and cortical atrophy in the bilateral parieto-occipital lobes
DWI/ADC	Detection of acute ischemic changes (useful within hours of onset)
CT (non-contrast)	Exclusion of acute intracranial hemorrhage
SPECT	Assessment of cerebral blood flow changes

MRI uses T1-weighted images to assess anatomical structures and T2-weighted images for high lesion detection.

Clues to Etiology

• Acute onset: Suggests cerebrovascular disease (including hypoperfusion).
• Painless and progressive: Suggests neurodegenerative disease.
• Focal symptoms + signs of increased intracranial pressure: Suggests tumor.

Referral from an ophthalmologist to a neurologist or neuro-ophthalmologist is important.

Q How is simultanagnosia detected in ophthalmology?

A

If a patient has normal color vision but cannot read numbers on the Ishihara color vision test, it is useful as a screening for simultanagnosia. Additionally, patterns where the patient cannot grasp the whole scene but only enumerates individual elements in complex visual scenes such as the Boston Cookie Theft picture also provide clues. It may be detected by confrontation testing even when quantitative perimetry is normal.

5. Standard Treatment

There is no fundamental drug therapy for simultanagnosia itself. Priority is given to treating the underlying disease and preventing progression of damage.

Treatment of Underlying Disease

• Cerebral infarction (acute phase): Consider ultra-early thrombolytic therapy with t-PA or endovascular treatment.
• Cerebral infarction (recurrence prevention): Use antiplatelet drugs (e.g., aspirin) and anticoagulants (e.g., warfarin).
• Tumor/cerebral hemorrhage: Surgery may be indicated in some cases.
• Alzheimer’s disease: Donepezil hydrochloride may be administered. ¹⁾

Rehabilitation

Low vision rehabilitation may improve symptoms of simultanagnosia. For visual deficits related to the central nervous system, there are rehabilitation approaches tailored to each symptom.

Precautions in treatment

Currently, there is no medication that improves simultanagnosia itself. The priority is appropriate management of the underlying disease and prevention of further damage, and early introduction of rehabilitation is important. When caused by progressive neurodegenerative disease, complete recovery is often difficult.

Q Can simultanagnosia be cured?

A

There is no fundamental cure, but treating the underlying disease to prevent progression of damage is important. In acute causes such as cerebral infarction, appropriate treatment and rehabilitation can lead to some improvement. When caused by progressive neurodegenerative disease, the prognosis is often poor, and early introduction of rehabilitation is recommended.

6. Pathophysiology and Detailed Mechanisms

The exact mechanism is unknown, but several hypotheses and neuroanatomical findings have been proposed.

Proposed Hypotheses

• Visuospatial attention deficit theory: The parietal lobe governs the visuospatial attention system, and its impairment prevents simultaneous perception of multiple stimuli.
• Object identification and location mismatch theory: Difficulty in grasping the whole occurs because the identity of an object and its position in the visual field do not match.

Two pathways of the higher visual cortex

There are two processing pathways in the higher visual cortex.

• Ventral stream (“what” pathway): Processes form and color vision in area V4.
• Dorsal stream (“where” pathway): Processes spatial location and motion vision in area V5. The dorsal stream to the parietal lobe handles spatial position perception.

Simultanagnosia occurs due to disruption of connections to the dorsal parietal lobe. The dorsal type results from damage to the dorsal pathway beyond area V4, while the ventral type is caused by damage to the occipitotemporal lobe.

Tau Protein Accumulation in Posterior Cortical Atrophy (PCA)

Tau protein accumulation and astrocytosis in the occipitotemporal lobe have been reported as pathological features of ventral-type PCA. ¹⁾

Shiio et al. (2024) reported a case of ventral-type PCA in a 73-year-old woman. MRI showed atrophy of the right fusiform gyrus, inferior occipital gyrus, and posterior inferior temporal gyrus. CSF examination revealed decreased Aβ1-42 (489.0 pg/mL), elevated total tau (625.7 pg/mL), and elevated phosphorylated tau (84.0 pg/mL). PiB-PET (amyloid) showed widespread distribution, while THK5351-PET (tau/MAO-B) showed localized accumulation in the occipitotemporal lobe. This suggests that tau protein accumulation/astrocytosis may be involved in the pathology of ventral-type PCA. ¹⁾

Amyloid β is widely distributed, but the site of tau accumulation was shown to correspond to clinical symptoms (visual recognition impairment in the ventral type).

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7. Latest Research and Future Prospects (Research Stage Reports)

For Patients: Please Read Carefully

The following content is currently at the research stage or under clinical trials and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Tau PET Imaging Research in PCA

Shiio et al. (2024) demonstrated that tau accumulation imaging using THK5351-PET is useful for elucidating the pathology of ventral-type PCA. ¹⁾ Tau accumulation was localized to the occipitotemporal lobe, anatomically consistent with the clinical symptoms of the ventral type. This finding aligns with the hypothesis that tau pathology, rather than amyloid plaques, is involved in the cognitive symptoms of AD. Although current AD treatments primarily target amyloid beta, this suggests the importance of therapies targeting tau. However, THK5351 binds not only to tau aggregates but also to MAO-B (monoamine oxidase B), making it difficult to strictly distinguish between tau accumulation and astrocytic gliosis, which is a limitation of this study.

No clinical trials or randomized controlled trials (RCTs) on treatments for simultanagnosia have been reported to date.

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8. References

1. Shiio M, Maeda N, Iwata A, et al. Ventral Variant Posterior Cortical Atrophy with Occipito-temporal Accumulation of Tau Proteins/Astrocyte Gliosis. Intern Med. 2024;63:2555-2565.
2. Primativo S, Starrfelt R. Definition: Simultanagnosia. Cortex. 2025;188:68. PMID: 40398205.
3. Carota A, Calabrese P. Simultanagnosia. Eur Neurol. 2011;66(1):6. PMID: 21646784.