Differences between cortical and subcortical dementia

When we talk about dementia, we mean a progressive global cognitive decline. Contrary to what many people may think, aging is not a cause of neurogenerative diseases and although there is comorbidity, there is no causality.

In fact, 30% of Parkinson’s patients have dementia, but the remaining 70% do not. But are all dementias the same? The answer is negative; there are two types of dementia, associated with different diagnoses. Therefore, in this article we will discuss the differences between cortical and subcortical dementia.

During the first half of the 20th century, dementia was equivalent to progressive intellectual deterioration. In 1987, the APA (American Psychological Association) established a diagnostic criterion: cognitive impairment had to be accompanied by a deterioration in memoryand for at least one of the following deficits: aphasia, apraxia, agnosia.

In 2012, the term dementia was eliminated, replacing it with neurocognitive disorder.

Alzheimer’s disease: cortical dementia

The differences between cortical and subcortical dementia begin with the location of the condition. In Alzheimer’s disease, the prototype of cortical dementia, there is a temporoparietal cortical predominance (Gustafson, 1992). Therefore, these dementias usually present deficits in short-term memory, episodic memory and verbal fluency.

Alzheimer’s disease, however, is not the only cortical dementia that exists; we find in turn Pick’s disease dementia or dementia with Lewy bodiesthe latter being the third cause of dementia, behind dementia due to Alzheimer’s disease and vascular dementia at the top.

Characteristics of cortical dementia

We will take Alzheimer’s disease as a reference to explain some of the consequences that cortical dementia can have on the cognition of those who suffer from it. We can stand out:

Short-term memory condition: short-term memory, which practically does not involve any cognitive operation, appears deficient. Tests like that of digit span present results that reflect a deterioration that is often related to the severity of the dementia.Episodic memory impairment: Within long-term memory, we find in cortical dementias an alteration of episodic memory. This is one of the most representative features of cortical dementia. It is the memory related to the retention of autobiographical events that occurred in one’s life.Verbal fluency within semantic memory: Also within long-term memory, difficulties are found in verbal fluency, that is, people with cortical dementias may find it random generate words within a semantic category. For example, if they are instructed to say words that may be included in the category “animal,” they will perform this task worse than if they are asked to generate words with a specific letter. This happens because this last task represents the phonological verbal fluencyand not the semantics.Naming problems: it is understood, based on their problems in verbal fluency, that patients with cortical dementia present problems naming objects. Therefore, tasks such as semantic associates (tiger for lion, or dog for cat) are performed poorly.

Parkinson’s disease: subcortical dementia

Among the differences between cortical and subcortical dementia we find that subcortical dementia develops in areas such as the basal ganglia or the hippocampus.

There are cognitive alterations insofar as the prefrontal area is massively connected to subcortical areas, and the condition of the latter implies a functional deactivation of the cortex.

Subcortical dementias par excellence are Huntington’s disease and Alzheimer’s disease. However, dementia does not always appear in these two conditions. In fact, only 20 to 30 percent of patients with Parkinson’s disease have sufficient diagnostic criteria to diagnose dementia.

The keys to subcortical dementia

On this occasion we will take Parkinson’s and Huntington’s disease to expose the main features of subcortical dementia. Some of them are:

Motor slowing: one of the main characteristics of subcortical dementia, unlike cortical dementia, is the presence of a serious motor disorder, characterized by slowing down and loss of balance. Although we will remember Parkinson’s or Huntington’s disease for resting tremor or chorea, respectively; The truth is that both subcortical dementias involve hypokinesis (minor mobility), akinesia (immobility) or bradykinesia (slow movements). This is also observed in the expressionless featuressince mobility in the face is also lost.emotional disturbances: In cortical dementias, emotional alterations may appear due to the assumption of the disease itself. In the case of subcortical dementias, these insidious changes in personality It can take years before dementia begins to express itself.. These people may be irritable, apathetic or have sexual disinterest, among others.Alterations in memory: in subcortical dementias there is a basic deficit in recovery. The big difference with cortical dementias is that in subcortical dementias, the the ability to learn new information.

The severity of cortical and subcortical dementia

Without a doubt, the differences between cortical and subcortical dementia are notable. Nevertheless, The great dissimilarity that we can find is the severity of both and its impact on the person’s daily life. Although not all of the alterations in both types of dementia have been exposed, we can observe a lesser cognitive deterioration in subcortical dementias than in cortical dementias.

The differences are not limited to the amount of cognitive impairment. These are also based on the non-presence, in the case of subcortical ones, of aphasias, agnosias and apraxias; something that does occur in cortical dementia.

Conclusions: two very different dementias

As a summary, it seems necessary to remember that the great differences between cortical and subcortical dementias are found in central executive abilities, memory and language. In the cortex, executive abilities such as preserved planning or problem solving, severe amnesia, and language with aphasic features are present.

In the case of subcortical dementias, these present very altered executive abilities from the beginning, memory with slight forgetfulness and language without aphasia, perhaps with excessive production. Both dementias converge in perceptive and visuospatial abilities. In both, these are altered.

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