The Differences Between Cortical and Subcortical Dementia

Are all dementias the same? The answer to that question is no, and we'll be telling you why in this article.

Dementias located in cortical areas won’t have the same impact on a person as those in subcortical areas. In this article, we’ll be looking at the differences between cortical and subcortical dementia.

When we talk about dementia, we mean progressive global cognitive impairment. Contrary to what many people may think, aging isn’t a cause of neurogenerative diseases. Although there’s comorbidity (the presence of one or more additional conditions), there’s no causality.

A curious fact is that 30 percent of Parkinson’s patients have dementia, but the remaining 70 percent don’t. But are all dementias the same? The answer is no; there are two main types of dementia, associated with different diagnoses. In this article, as we mentioned above, we’ll be talking about 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 American Psychological Association (APA) established diagnostic criteria. They stated that cognitive impairment had to be accompanied by a deterioration in memory, and by at least one of the following deficits: aphasia, apraxia, or agnosia.

In 2012, the term dementia was eliminated and replaced by neurocognitive disorder.

Alzheimer’s disease: cortical dementia

The differences between cortical and subcortical dementia begin with the origin of the condition. In Alzheimer’s disease, the prototype of cortical dementia, there’s a cortical temporoparietal predominance (Gustafson, 1992). Because of this, these dementias often cause deficits in short-term memory, episodic memory, and verbal fluency.

Alzheimer’s disease, however, isn’t the only cortical dementia that exists. We also find dementia caused by Pick’s disease or Lewy body dementia. The latter is the third cause of dementia, behind Alzheimer’s disease and vascular dementia.

The characteristics of cortical dementia

Let’s take Alzheimer’s disease as a point of reference in order to explain some of the consequences of cortical dementia on the cognitive processes of those who suffer from it. Doctors highlight the following processes:

• Short-term memory condition. The short-term memory, which carries out practically no cognitive operations, is shown to be deficient. Numerical tests can give results that show a deterioration that’s often related to the severity of the dementia.
• Deterioration of episodic memory. Within long-term memory, in cortical dementia, there’s an alteration in episodic memory. This is one of the most common characteristics of cortical dementia. We’re talking here about the memory that retains autobiographical events in one’s life.
• Verbal fluency within semantic memory. Also within long-term memory, there are difficulties with verbal fluency. People with cortical dementia may find it difficult to name words within a particular semantic category. For example, if someone asks them to say words that fall into the category “animals”, then they’ll perform that task worse than if that same person had asked them to say words that start with the same letter. This is because the second task deals with phonological verbal fluidity, not semantics.
• Naming problems. As we mentioned above, patients with cortical dementia have problems naming objects. Therefore, they have problems doing tasks involving semantic associates (tiger for lion or dog for cat, for example).

Parkinson’s disease: subcortical dementia

Among the differences between cortical and subcortical dementia, specialists have shown that subcortical dementia develops in areas such as the basal ganglia or the hippocampus.

It causes changes in a patient’s cognitive functions. The prefrontal area of the brain is closely and widely connected to subcortical areas. The condition of the latter implies a functional deactivation of the cortex.

The typical subcortical dementias are Huntington’s disease and Alzheimer’s disease. However, dementia doesn’t always manifest in these two conditions. In fact, only 20 to 30 percent of patients with Parkinson’s disease have sufficient diagnostic criteria to be diagnosed with dementia.

The keys to subcortical dementia

We’ll now take Parkinson’s and Huntington’s diseases to explain the main characteristics of subcortical dementia. Some of them are:

• Motor impairment. One of the main characteristics of subcortical dementia, unlike cortical dementia, is the presence of a severe motor disorder, characterized by the patient slowing down and suffering a loss of balance. Although you’ll surely associate Parkinson’s or Huntington’s diseases with a shaking of the hands, or chorea, the truth is that both subcortical dementias involve hypokinesia (minor mobility), akinesia (immobility), or bradykinesia (slow movements). There’s also an inability to express themselves facially, as the person also loses facial mobility.
• Emotional changes. In cortical dementias, emotional changes may appear as the person comes to terms with the disease. In the case of subcortical dementias, these changes in personality can occur years before the dementia begins to manifest. These people may become irritable, apathetic, or sexually disinterested, among other things.
• Memory disorders. In subcortical dementias, there’s a basic memory recovery deficit. The big difference with cortical dementias is that, in subcortical dementias, the patient maintains the ability to learn new information for a long time.

The severity of cortical and subcortical dementia

As we’ve seen, there’s a substantial difference between cortical and subcortical dementia. However, the main difference is their severity, and how they impact a person in their daily life. Although we haven’t mentioned all the symptoms in both types of dementia, we can highlight a lower cognitive impairment in subcortical dementias than in cortical ones.

The difference here isn’t only the degree of cognitive impairment. The other major difference is that, in subcortical dementia, the patient doesn’t suffer from aphasia, agnosia, or apraxia, something that does occur in cortical dementia.

Conclusion: two very different dementias

In conclusion, the major differences between cortical and subcortical dementias are found in executive functions, memory, and language. However, in cortical dementia, the executive functions such as planning or problem solving are retained but accompanied by severe amnesia and verbal expression with signs of aphasia.

In the case of subcortical dementias, the executive functions are affected right from the beginning: slight forgetfulness and a language without aphasias, but perhaps an excessive desire to talk. Both dementias affect perceptual and visuospatial capacities.