Inhibition (Slowing) of Thinking

Inhibition of thinking is a marked slowing in the pace at which thoughts and mental images arise, so that the person finds it harder to concentrate, make decisions, or think clearly. It is often felt by the person as a kind of mental fog or heaviness, sometimes described as a strange sensation in the head, which can make it difficult to tell whether they are describing a physical or a psychological problem.

This has traditionally been framed less as an absence of thought and more as a genuine slowing in its rate and richness, distinguishing it from thought blocking, in which the train of thought stops entirely and abruptly rather than merely running more slowly.

Recognition features

A subjectively and objectively slowed pace of thinking, with fewer thoughts and mental images arising over a given period
Reported difficulty concentrating, making decisions, and keeping thoughts clear
Reduced active attention, leading to poor registration of events and complaints of poor memory
May be accompanied by a vague, hard-to-describe unpleasant sensation 'in the head'

Eliciting it at interview

Ask directly: "Do your thoughts feel like they're moving more slowly than usual, as though it's harder to think things through?"
Ask about downstream effects, such as difficulty concentrating on reading or television, or trouble making everyday decisions
Where a memory complaint is prominent, explore carefully whether it reflects true memory impairment or the poor registration that comes with slowed, inattentive thinking, since the distinction matters for diagnosis

Distinguishing features

Differs from thought blocking, which is a sudden, complete stop in the train of thought rather than a general slowing of its pace
Differs from a true dementia, which involves genuine memory and cognitive impairment rather than a reversible slowing tied to mood state
In depression, the accompanying complaint of poor memory can closely mimic early dementia, making careful assessment of mood and reversibility important

Common misconceptions

That a depressed patient complaining of poor memory and confusion necessarily has a degenerative brain disease; this presentation is well recognised in depression and can improve substantially as mood improves
That slowed thinking always reflects passivity or lack of effort; the person is often distressed by the change and struggling actively against it

Related phenomena

Thought Blocking · Anxiety Amnesia · Depressive Pseudodementia

Practice this

A depressed patient describes his thoughts as coming slowly and with effort, complaining of a mental fog that makes it hard to concentrate or make even small decisions, a pace that has gradually worsened over weeks. What is this? · Mid-sentence, describing his weekend, a patient suddenly stops speaking entirely, looking momentarily blank, and afterward cannot recall what he had been about to say, though his speech had been at a completely normal pace right up until that moment. Before revealing the answer: is this inhibition of thinking? · A patient's thinking seems disrupted. Before revealing the answer, decide what distinguishes inhibition of thinking from thought blocking. · You suspect a depressed patient shows inhibition of thinking. Before revealing the answer, decide how you would assess for this. · Explain why inhibition of thinking can be mistaken for early dementia, and why this distinction matters clinically.

Illustration

A 58-year-old man with severe low mood describes needing to reread the same newspaper paragraph five or six times before any of it registers, and says that choosing what to have for lunch now feels like an exhausting task that leaves him mentally drained, whereas six months ago it would not have crossed his mind as a difficulty at all.

References

Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 4, 'Disorders of Thought and Speech'.