I O N E F I N E

Almost one-quarter of the brain is normally devoted to processing visual information: reading text, recogniz-

ing faces, following the Sunday match, and much more. The brain’s visual cortex contains specialized regions devoted to process-ing motion, text, faces, scenes, objects and even the position and movement of bodies. In congenitally blind individu-als, much of the ‘visual’ cortex responds strongly to auditory and tactile input rather than to visual stimuli, a phenom-enon known as cross-modal plasticity. Writing in Current Biology, Striem-Amit and Amedi1 shed light on how these cross-modal responses are organized.

The researchers trained congeni-tally blind individuals for 70 hours in the use of a technology2 that converts visual information into ‘soundscapes’ (called vOICe). After an initial click, an image frame is scanned from left to right and then represented by a sequence of ‘chords’. Brightness is represented by loudness, height in the scene is repre-sented by pitch and horizontal position is represented by the time since the click. For example, a diagonal line stretching upward from left to right becomes the sound of an ascending sweep.

The authors used functional magnetic resonance imaging to measure the brain responses of participants while they listened to soundscapes of body-shape silhouettes, objects, faces and abstract patterns. These brain responses were compared with those of sighted individ-uals viewing the corresponding visual images. Both blind and sighted subjects showed larger responses to body-shape silhouettes than to other images within

a region of the brain known as the extrastriate body area (EBA), which, in individuals with normal sight, is involved in visual perception of the human body.

One of the most interesting conclusions that Striem-Amit and Amedi draw from their results is that the specialization for body-shape

information in the EBA is innate, requiring little experience to develop, because selectivity for body-shape silhouettes in this brain area occurs even in blind individuals with little or no experience of body shape before training with vOICe. Thus, the authors interpret their findings as evidence that the specialization found in the visual cortex may exist indepen-dently of experience.

This claim is based on the assumption that congenitally blind individuals have a deeply impoverished experience of others’ body pos-tures, actions and movements. Indeed, the authors claim that this information is avail-able to blind individuals solely through touch, and that they have no auditory experience of body shape before vOICe training. However, in the course of our research, my laboratory

has noticed that many visually impaired individuals report knowing a surprising amount about body positions, actions and intents from sound alone. Visually impaired subject Mike May reports: “I know when people are getting bored by my presentation because I can hear them shuffling in their chairs.” A fully blind col-league, Nick Giuduce, admits: “When I’m interested in a woman, I can tell if she’s slender by how much the floor creaks as she walks by.” Amy Burk, the Cana-dian goalball player shown on the right in Figure 1, reports: “I can see it all … I can visualize it all … if they are moving with the ball I’m moving with them … whatever side they are going on I’m following the person.” It is reasonable to suggest that the EBA has a role in inter-preting these auditory experiences in blind individuals.

Regardless of whether auditory experience before training with vOICe involves the EBA, this study adds to a body of work suggesting that ‘functional constancy’ is one of the organizational principles underlying cross-modal plasticity in blind people3. According to this principle, specialized brain regions continue to serve the same function in blind individuals, but there is a shift in the regions’ primary sensory input from sight to hearing or touch. A variety of studies have provided evidence for func-tional constancy in blind individuals. These showed that the visual-motion

predicting fossil-fuel prices, renewable-energy production costs, and incentives (such as car-bon taxes) to use renewables in place of fossil fuels, the timetable for widespread adoption of renewable fuels is not clear. But the production of fuels from non-fossil sources will certainly require effective catalysts. Li and colleagues’ work is an excellent step in that direction. ■

Aaron M. Appel is in the Catalysis Science

Group, Pacific Northwest National Laboratory, Richland, Washington 99352, USA. e-mail: aaron.appel@pnnl.gov

1. Li, C. W., Ciston, J. & Kanan, M. W. Nature 508, 504–507 (2014).

2. Hori, Y. in Modern Aspects of Electrochemistry Vol. 42 (eds Vayenas, C. G. et al.) 89–189 (Springer, 2008).

3. Cook, T. R. et al. Chem. Rev. 110, 6474–6502 (2010).

4. Olah, G. A., Prakash, G. K. S. & Goeppert, A. J. Am.

S E N S O R Y S Y S T E M S

Do you hear what I see?Researchers have found evidence that the representation of auditory and tactile information in the brains of blind people shows strong similarities to the way in which visual information is represented in sighted people.

Figure 1 | Using sound instead of sight. In goalball, a sport designed for blind athletes, players use sound to determine the position of both the ball and the other players. Striem-Amit and Amedi1 report that auditory stimuli are processed in blind people by a region of the brain that is associated with vision in sighted individuals.

CLI

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Chem. Soc. 133, 12881–12898 (2011).5. Kondratenko, E. V., Mul, G., Baltrusaitis, J.,

Larrazábal, G. O. & Pérez-Ramírez, J. Energy Environ. Sci. 6, 3112–3135 (2013).

6. Thoi, V. S., Sun, Y., Long, J. R. & Chang, C. J. Chem. Soc. Rev. 42, 2388–2400 (2013).

7. Li, C. W. & Kanan, M. W. J. Am. Chem. Soc. 134, 7231–7234 (2012).

8. Appel, A. M. et al. Chem. Rev. 113, 6621–6658 (2013).

This article was published online on 9 April 2014.

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Early in an immune response, antigen molecules are captured by antigen- presenting cells and displayed on the

cells’ surface, where they are recognized by receptors on the surface of lymphocytes (B cells, T cells and natural killer cells)1,2. The lymphocyte then becomes joined to the antigen-presenting cell and extracts these sur-face mol ecules along with patches of the cell

membrane. This process, termed trogocyto-sis (from the Greek word trogo, to nibble)2,3, activates the lymphocyte to initiate a specific immune response to that antigen. Until now, trogo cytosis had been observed only between immune cells. But in this issue, Ralston et al.4 (page 526) describe a form of trogocytosis carried out by the parasite Entamoeba histo-lytica, and suggest that this process mediates the destruction of intestinal cells that is seen in amoebiasis — the gastro intestinal infection

caused by these unicellular organisms. Trogocytosis in immune cells requires the

transduction of signals from the acceptor-cell surface by means of kinase enzymes such as Src, Syk and PI3K, and by modulation of the cell’s cytoskeleton (which is rich in the pro-tein actin) and of intracellular calcium-ion (Ca2+) levels2,5. It is a rapid process, occurring within minutes of co-culturing the participant cells in vitro2. Notably, despite the exchange of mater ial, neither the antigen-presenting cell nor the lymphocyte dies following trogo cytosis.

In the first description of the process3, it was proposed that trogo cytosis may have evolved as a way for cells to acquire nourishment from other cells, and later as a means of intercellular communication. The hypothesis of an ancient origin for trogocytosis is now supported by Ralston and colleagues’ observation of a simi-lar mechanism in E. histolytica, an ancient organism. However, unexpectedly, this form of trogocytosis enhances the parasite’s virulence,

area of the brain responds to auditory and tactile motion4–6, that sounds made by objects are represented in brain regions associated with visual-object recognition7,8, and that read-ing Braille elicits brain responses in the visual word-form area9.

There is an appealing elegance to the idea that the representation of auditory and tactile information in the ‘visual’ cortex of blind individuals is analogous to that of sighted people. But the extent of the apparent similar-ity may be partly a consequence of hypoth-eses being tested from a sighted perspective. Experiments published so far have relied on measuring brain responses to auditory stim-uli that have been experimentally selected and categorized on the basis of what makes intuitive sense to us as sighted scientists. This may result in an overemphasis of apparent similarities.

More-detailed examination of the response profiles of seemingly analogous areas of the brain using a wider variety of stimuli may yet reveal important differences between blind and sighted individuals, both in the way that information is represented and in the function of these areas with respect to perception and behaviour. Indeed, in their discussion, Striem-Amit and Amedi note that the representation of bodies is not identical in blind and sighted individuals. A second region of the brain that seems to represent body shape, the fusiform body area (which may contain a more holi-stic representation of body position), showed reduced selectivity to body-shape information in the blind individuals they studied. More over, the intriguing possibility that blind people have specialized regions that contain representations of the world with no sighted equivalent remains almost entirely unexplored. ■

Ione Fine is in the Department of Psychology, University of Washington, Seattle, Washington 98195, USA.e-mail: ionefine@uw.edu

1. Striem-Amit, E. & Amedi, A. Curr. Biol. 24, 687–692 (2014).

2. Meijer, P. B. L. IEEE Trans. Biomed. Eng. 39, 112–121 (1992).

3. Pascual-Leone, A. & Hamilton, R. in Progress in Brain Research Vol. 134 (eds Casanova, C. & Ptito, M.) Ch. 27, 427–445 (Elsevier, 2001).

4. Poirier, C. et al. NeuroImage 31, 279–285 (2006).5. Saenz, M., Lewis, L. B., Huth, A. G., Fine, I. & Koch, C.

J. Neurosci. 28, 5141–5148 (2008).6. Bedny, M., Konkle, T., Pelphrey, K., Saxe, R. &

Pascual-Leone, A. Curr. Biol. 20, 1900–1906 (2010).

7. Mahon, B. Z., Anzellotti, S., Schwarzbach, J., Zampini, M. & Caramazza, A. Neuron 63, 397–405 (2009).

8. Amedi, A. et al. Nature Neurosci. 10, 687–689 (2007).

9. Striem-Amit, E., Cohen, L., Dehaene, S. & Amedi, A. Neuron 76, 640–652 (2012).

ContactHost

Parasite PrimingSrc, Syk, PI3K

Pinch Ingestion Ampli�ed ingestion

Cell death

Carbohydrate chain

Glycoprotein

Figure 1 | Amoebic trogocytosis. Ralston et al.4 have described trogocytosis by Entamoeba histolytica, in which the parasites tear off and ingest patches of host cells, resulting in their death. The interaction between the cells is mediated by abundant surface molecules, including glycoproteins and their attached carbohydrate chains. The cell-to-cell contact is then stabilized through adhesion molecules (not shown), and cytoskeletal activity in the

parasite is probably involved in generating the force required to pinch off the host-cell membrane. This transfer of cellular material causes changes in intracellular calcium-ion levels and triggers signalling pathways in both cells. The activity of Src, Syk and PI3K enzymes contributes to this process and leads to ‘priming’ of the parasites, which amplifies subsequent ingestion. After successive nibbling events, the host cell dies and the parasite moves on.

I N F E C T I O N B I O L O G Y

Nibbled to death Trogocytosis, a process in which one cell ‘takes a bite’ out of another, had previously been seen only in immune cells. But the phenomenon has now been found in Entamoeba histolytica, as a way for this parasite to kill host cells. See Letter p.526

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