Sedatives, shock, and toxæmia, by lowering the level of consciousness, delay the appearance of the phantom.

Impact of Sedatives on Phantom Perception

The weather has been noted to have a marked influence on the vast majority of phantoms, in that they are more noticeable in winter (especially during a cold spell). This is the most enduring influence and it persists long after other inducing and intensifying factors have ceased to be effective. In fact, after two or three years the phantom may be noticed only when there is a "change in the weather."

Impact of Climatic Conditions on Phantom

Henderson and Smyth's study found that patients could at first evoke the phantom, temporarily, by merely thinking about it. This voluntary direction of thought was, like other factors, at first uniformly effective, but it did become gradually weaker and finally would disappear. It is one of the more enduring influences.

Thinking of the Phantom

There is a brief sensation in the stump/phantom during urination in at least 90% of thigh and leg amputations, usually mild or unnoticed. The sensation is one of two kinds, either a tingling in the phantom or a tingling on the end of the stump w/o any reference to the phantom. This rarely, if ever, occurs in upper limb phantoms.

The Effect of Urinating on the Phantom

When a patient stumbles or slips on crutches a strong sensation shoots down the limb, with the phantom being felt momentarily. Simultaneously, the stump moves out as if to save the patient from falling. This has been noted as one of the more enduring reflexes.

Effect of Loss of Balance on Phantom

When the stump begins to move to complete a task (like picking up a ball), the mistake in attempting to use the phantom limb is realized and simultaneously there is often, but not always, a monetary sensation of the phantom (however this ceases within a few months for the patients "quickly learn to avoid making mistakes"). One possible explanation for this is that the cortex is in a hypersensitive state, enabling the normally subconscious reflexes locally to reach a conscious level.

Effect of Instinctive Actions on Phantom

Sudden fright (ie. from a loud noise) is sometimes associated with momentary perception of the phantom.

Effect of Fright on Phantom Perception

Emotion such as anger or excitement makes the patient forget the phantom.

Effect of Emotion on Phantom Perception

Nearly 100 men were fitted with temporary limbs nine to eighteen months after amputation. Almost without exception the phantom was never felt while wearing the prosthetic but often reappeared when it was removed. 

Effect of Wearing an Artificial Limb on Phantom Perception

Following an amputation, severe pain in the stump can initially overshadow the perception of a phantom limb. Consequently, during the healing process, there may be a delay of several weeks before the phantom limb is perceived. One theory suggests that this delay occurs because the patient's attention is diverted from the phantom limb by the severe pain in the stump.

Effect of Stump Pain on Phantom Limb Perception

There are a number of factors that may impact the degree to which a patient detects the tingling, or phantom-like, sensation.
- Pain in the Stump
- Sedatives
- Climatic Conditions
- Thinking of Phantom
- Urinating and other Visceral Reflexes
- Loss of Balance
- Instinctive Actions
- Fright
- Emotion
- Attachment of Artificial Limb

Johns Hopkins University

- Statistics from the Study
- Natural Phantoms
- Telescoping
- Course of the Phantom
- Impression of Voluntary Movement
- Automatic Knee Movements
- Factors that Affect Phantom Perception
- Relationship of Phantom to Solid Structures

Henderson and Smyth "Phantom Limbs" Study (1940)

HENDERSON, W. R., & SMYTH, G. E. (1948). Phantom limbs. Journal of neurology, neurosurgery, and psychiatry, 11(2), 88–112. https://doi.org/10.1136/jnnp.11.2.88

HENDERSON, W. R., & SMYTH, G. E. (1948). Phantom limbs. 

Whether or not a patient can, and the degree to which they can, "move" certain components of the phantom depends on two factors:
1. The level of the amputation
2. Degree of sensory awareness of the various joints
In forearm amputations, the digits can at first be moved in every phantom. However with lower limbs, the phantom is weaker and "movements" are more difficult to produce. 

"Voluntary Movement" of Phantom Limbs

More than 10% of patients observed that their phantom knee sometimes moved spontaneously as much as 90 degrees "just automatically." These automatic changes could not be voluntarily initiated or prevented. 

Automatic Knee Movements in Phantoms

In total, "some three hundred major and many minor amputations" were observed in this longitudinal study. A minority of of men (~10%) could identify "well-marked" phantoms, had made original observations, and could describe their impressions clearly. The majority of men (~80%) had a typical phantom that "had been so mild and unobtrusive" and had given "little thought to it" prior to the study (dubbed the "average phantom"). The remaining men (~10%) felt vague tingling, did not perceive a phantom.  

Statistics from the Henderson & Smyth Study (1948)

The "natural phantom" is defined as the almost invariable appearance in consciousness of the missing limb/part. As observed by Henderson and Smyth, it is usually associated with a positive sensation described as tingling or numbness. In the context of the study, this "tingling" sensation was always stronger than any vague awareness of an intact limb. 

The "Natural Phantom"

Telescoping refers to the phenomenon observed in the phantom limb patients where patients perceived digits gradually approaching the stump and almost becoming "attached" it. This presumably resulted from the weakening of the phantom, or specific parts of it. The time at which shortening begins is variable, though the rate of telescoping appears to be related to the strength of the phantoms.

Telescoping

Factors that Affect Phantom Perception

Phantoms are often perceived when the patient awakens from the anesthetic and there is nothing unusual detected about the sensation. At first, the phantom is felt continuously. After a few weeks, the tingling becomes weaker and recurs less frequently. During the next six to twelve months, the phantom weakens considerably. The average phantom is mild and rapidly subsided, however.
- Relation Between Cerebral Structures and Phantom

Course of Natural Phantom

Patients perceived phantom to pass through solid structures unimpeded and without arousing any feeling of obstruction or unpleasant sensation; mostly observed in upper limbs; only exception is when strong phantom digits (attached to stump through telescoping) appear to occupy a space that "does not exist"

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