|Year : 2015 | Volume
| Issue : 1 | Page : 3-5
The phantom breast after mastectomy, the homunculus and the hole in the cortical map
Department of Clinical Neurosciences, Neuropsychology Research Division, Bengaluru, Karnataka, India
|Date of Web Publication||16-Apr-2015|
ACRO, Dr. Balabhai Nanavati Hospital, S.V. Road, Vile Parle (W), Mumbai - 400 056
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Dutta V. The phantom breast after mastectomy, the homunculus and the hole in the cortical map. J Can Res Ther 2015;11:3-5
A little bit of Wilder Penfield's homunculus (the little man) might help us understand why the phantom breast phenomenon is shrouded in mystery at the cortical level. When multiple versions of the homunculus started appearing in the form of Cantlie's illustrations in the 50s, Penfield started coming under sharp criticism, FMR Walsh chided him for "this shift from being a cortical cartographer to someone who kept evolving novel anthropomorphic figures." 
More than the scathing attacks of the homunculus misrepresenting most of our anatomy; the little man was mired in guilt for not having represented the female anatomy at all, so much so that even though the breast never appeared in Cantlie's original sketches, almost 25% of the texts studied in 1987 show a homunculus with a breast, a detail attributed to Norman Geschwind. 
One reason the phantom breast phenomenon is so shrouded in mystery after mastectomies, unlike the phantom limb syndrome; is perhaps because of the limited area it covers in the somatosensory cortex. 
It was Krøner et al., , who first mentioned the difference between phantom breast sensation (PBS), and phantom breast pain, the former experienced as sensations in the amputated breast that was not as severe and painful as the latter endured as intense pain after mastectomy. Numerous studies have prevailed upon this phenomenon, enough to augur the necessary exploration of this unusual phenomenon in the somatosensory cortex.
Almost 33% of the women undergo cortical re-mapping of the breast after mastectomy.  Some studies have allowed us depth into the functional side of neural plasticity following mastectomy even just a few days postsurgery  but very little is known about how it works in tandem with the somatosensory cortex. A few studies have shown how women after mastectomy have experienced PBS along with other symptoms. A cross-sectional study by Hansen et al.,  showed how younger women were in fact reporting more symptoms of PBS than older women. Almost 34% of the younger women in the study group reported this phenomenon. PBS was experienced even 1-3 years after surgery in 26% of the patients that corroborates with research done in the past by Aglioti et al.  PBS was perceived even 12 years postsurgery.
Dijkstra et al. 2007  in an in-depth analysis of the methodology used in most research designs found that cross-sectional studies reported a higher occurrence of PBSs than PB pain when compared to prospective studies (PBSs was averagely 8% lower, and PB pain was 9% higher when compared to the cross-sectional group). They examined 29 studies with a large number of women (2052 women were assessed for PBSs and 1293 for PB pain); of which 23 studies were cross-sectional, and 6 were prospective. Their findings indicated a sharp trend towards a bias in the experimental design chosen, which sends out a cautionary note to future studies too.
Differences between the interview and the questionnaire approach too were observed where PBS and PB pain in the interview method was reportedly 5% lower than the latter approach. A crucial observation made was that women who were amputated at a younger age were more susceptible to experiencing PBSs than those who underwent mastectomy at a later period in their lives. 
Aglioti et al.'s  analysis of the "referred sensation" of the missing breast by women after their breasts were amputated led them to the "perceived phantom sensation" of the amputated breast in these women when they were stimulated on their ipsilateral body part proximal to where the breast is represented in the SS. The authors also found that this "phantom sensation" could appear as early as 5 days after surgery and in a few cases, some women were enduring the phantom for as long as 12 years. ,
Among the 15 patients who reported PBS, 5 women who were persistently experiencing PBS during the experimental session reported an evoked sensation of the phantom when the pinna was stimulated, something that was not reported by any patient prior to their mastectomy. The phantom sensation in the breast mainly involves the nipple which is the area most extensively represented in the brain.  It would be interesting to explore the topography of the skin regions that evokes the phantom sensation, since they are both intricately linked and because of the complex "modality-specific re-mapping" involved, the re-organization that takes place has been attributed to the central nervous system. 
Even when the nervous system is at its inceptive stage in utero, its neuronal growth is greatly determined by hormones and sex differences. , Underscoring the need to investigate the somatosensory cortex and its little games in organizing and re-organizing in both males and females. Studies have shown sex differences in healthy as well as the diseased nervous system when both adult male and female cortical responses to sensory stimuli were compared directly,. 
A few brain re-mapping studies in humans and rodents have given us a glimpse of how some crucial events in a woman's life can alter the cortical and dendritic representation in the brain such as nursing,  mastectomy  and lower limb amputation.  Hence, from what we know about how neural plasticity works in recent decades through precision neuroimaging studies it gives us more reason to take the homunculus with a pinch of salt. 
From the few studies discussed significant aspects emerge, like how the change in therapeutic procedures over the years has influenced the reporting of PBS in the first place. The reason for fewer citations in recent years being the use of radical surgical procedures like modified radical mastectomies where the major and minor pectoral muscles are spared. 
Another observation made by Dijkstra et al.,  is how a number of co-morbid factors decide the way in which research gets interpreted, firstly the research design adopted by most studies, such as cross-sectional versus the prospective study design, the assessment method adopted, the age at which the symptoms first appeared, along with the intermittent period between postoperative period and the appearance of PBS, the time interval between the mastectomy and the time when research took place, which was inappropriately described in most studies.
When one is considering the assessment approach, it is important to frame qualitative research methods since there can be no gold standard in the way research studies are designed because of the diversity in this population. Including the patient narrative through semi-structured interviews would be the first step in steering them out of their reluctance to talk about the phantom breast phenomenon and the apprehensions and anxiety that chance along with it.
The most striking part of this phenomenon described was the rapidity in which sensory re-mapping took place within days of surgery  and how 12 years postmastectomy could also trigger the phantom. ,
Considering the topography of the skin region that elicits the phantom, it would be useful to design studies that examines the modality-specific re-organizational processes suggesting the ubiquitous role of the central nervous system as shown by Aglioti et al. , The propensity of younger women to report this phenomenon more often than older women who have undergone mastectomy at a later stage in their lives equally implicates the need to further exploration in this area. ,
What Penfield tried to give us was a map of some unknown terrain in a mysterious country he called "the brain".  He mentioned "… The exact position of the parts must not be considered topographically accurate. They are aids to memory, no more (…) the figurines have defects and virtues of cartoons in that they are inaccurate anatomically." 
The homunculus is not there to verify each and every attribute of its topography and current literature is full of evidence for cortical and dendritic plasticity in females of both humans and rodent species during crucial phases of their lives, ,, and as mentioned by Di Noto et al. 2013, a more enterprising foray into the exploration of this cortical depth would be to chalk out a new map for the homunculus. Hence, it seems right to suggest that one took this little man just as the rough map as suggested by Penfield himself and continue drilling into the anthropomorphic depths of this undomesticated terrain.
| > References|| |
Pogliano C. Penfield′s homunculus and other grotesque creatures from the Land of If. Nuncius 2012;27:141-62.
Aglioti S, Cortese F, Franchini C. Rapid sensory remapping in the adult human brain as inferred from phantom breast perception. Neuroreport 1994;5:473-6.
Krøner K, Krebs B, Skov J, Jørgensen HS. Immediate and long-term phantom breast syndrome after mastectomy: Incidence, clinical characteristics and relationship to pre-mastectomy breast pain. Pain 1989;36:327-34.
Krøner K, Knudsen UB, Lundby L, Hvid H. Long-term phantom breast syndrome after mastectomy. Clin J Pain 1992;8:346-50.
Di Noto PM, Newman L, Wall S, Einstein G. The hermunculus: What is known about the representation of the female body in the brain? Cereb Cortex 2013;23:1005-13.
Hansen DM, Kehlet H, Gärtner R. Phantom breast sensations are frequent after mastectomy. Dan Med Bull 2011;58:A4259.
Dijkstra PU, Rietman JS, Geertzen JH. Phantom breast sensations and phantom breast pain: A 2-year prospective study and a methodological analysis of literature. Eur J Pain 2007;11:99-108.
Aglioti SM, Cortese F, Franchini C, Zamboni S. Phantom breast as perceptual correlate of neuroplasticity in adult human brain. Soc Neurosci Abstr 1993;19:702.13.
Chen JR, Yan YT, Wang TJ, Chen LJ, Wang YJ, Tseng GF. Gonadal hormones modulate the dendritic spine densities of primary cortical pyramidal neurons in adult female rat. Cereb Cortex 2009;19:2719-27.
Kordower JH, Chen EY, Morrison JH. Long-term gonadal hormone treatment and endogenous neurogenesis in the dentate Gyrus of the adult female monkey. Exp Neurol 2010;224:252-7.
Cahill L. Why sex matters for neuroscience. Nat Rev Neurosci 2006;7:477-84.
Xerri C, Stern JM, Merzenich MM. Alterations of the cortical representation of the rat ventrum induced by nursing behavior. J Neurosci 1994;14:1710-21.
Aurbach E, Heller L, Eagleman D. Plasticity of somatosensory cortex after surgical body recontouring. Soc Neurosci Abstr 2009;39:363.25.
Aglioti S, Bonazzi A, Cortese F. Phantom lower limb as a perceptual marker of neural plasticity in the mature human brain. Proc Biol Sci 1994;255:273-8.