Agnostic Brain, Biased Mind - what does the FFA do?

Many neuroimaging studies have repeatedly found an area in the human brain that seems to be involved in processing visual faces. This area located in the fusiform gyri in humans, has been affectionately named the fusiform face area or FFA. The FFA is most active when we are looking at pictures of faces, and almost non-responsive to other types of visual items such as objects, houses, scenes, random textures, or a blank screen. Prosopagnosics, who are not able to recognize faces, but are still able to detect the presence of a face and also show no difficulty in processing other types of visual stimuli, have been shown to involve less FFA activity. Even more compelling, patients with lateral occipital lobes lesioned lose some form of object-processing, but show intact face processing. And yet other patients with lesions that have affected the FFA, have problems with face processing (acquired prosopagnosia) but intact processing for other stimuli. The evidence strongly suggests that there is something special about faces, and something about the FFA that deals with this specialization.

The debate regarding the FFA pertain to whether it is the only region or even a critical region that does face processing. Some labs have shown that face processing information can be found in other regions of the brain that are not the FFA. Yet some labs have shown that the FFA is recruited to process fine levels of category distinctions. For example, bird and car experts have been shown to engage some level of FFA activity when processing these stimuli compared to novices. These findings suggest that the FFA is not processing faces per se, but visual representations that have come to require high-levels of fine discrimination through experience, of which faces are the best example of this currently.

I suggest that a more flexible definition is called for when thinking about the FFA and its role in processing visual information. Certainly, it does seem that faces occupy a special place in human experiences. On the other hand, it is difficult to explain why there would be a brain region that codes for faces and faces along based simply based on genetic or biologically determined causes.

In terms of a neural network, if indeed the brain consists of many different sub-types of neural networks that conglomerate to form one large complex network, the FFA is a sub-network specialized to perform a specific operation that is maximized and specialized (trained) for a specific information domain - faces. This or these specific operation(s) could involve identification, discrimination, recognition, or all of these, or even a yet unknown operation. Certainly neural network non-linearities can surprise us! Moreover, these operations have been tuned for a specialized class of stimuli that consists of eyes, nose, mouths, and other visual characteristics of faces when occurring together as a whole (whether from external input, or through internal imagination or retrieval).

What this means is that if you were able to "remove" the FFA, and plug it into a computer so that you can feed this FFA network with inputs and measure its outputs, you could theoretically feed it anything, but the information would be most meaningful or organized when the inputs correspond to information about a face. Of course, this would require us to know what is the language of the input to perform such an experiment.

Other types of inputs may elicit some level of meaningful output of the FFA. Neural network do that. Yet other types may elicit nothing at all. This does not necessarily mean that the FFA outputs from such inputs is useless, nor does necessarily mean that it is used! It is just output. What higher-level brain mechanisms do with the output depends on the task, and how the brain is wired to treat outputs from its sub-networks. It may be ignored, or it may actually incorporate relevant information. That is, the FFA is agnostic to the incoming information. It does not care. It will process it anyway. But other regions decide whether what is it saying needs to be incorporated or not, or if it should be further modified even.

Such a view would reconcile why the FFA is special for faces, yet seems to be carrying some information about other stimuli. It would also be consistent with the idea that information about faces is certainly also available to a certain extent in non-FFA regions, the same principles being applied to these other sub-networks. It would also be consistent with how self-organizing behavior in neural network (see von der Malsburg article [link]) can lead to a consistent topology across every person that processes a particular stimulus in a particular way in a particular spatial location.

This is probably not a new idea, but needs to be clarified in the literature I think.

Default Network, Meditation, and Focus Training

A recent study found that teaching children to focus improves their health outcome [ScienceDaily report]. In relation to the default network in the brain, perhaps one of the things that such early training does is to improve the individual's ability to regulate default network activity. DN activity has been linked to self-reflection, self-monitoring, day-dreaming, task-unrelated thoughts etc., and has often been seen to be negatively correlated to one's ability to perform a task. That is, the more you are able to disengage your default network, the better you can perform the task. This is presumably because your attention is more focused and not distracted by task-unrelated thoughts.

It is then not hard to see the link between DN activity regulation and meditation. Meditation is an act of self-regulation of thoughts, and has been related to several positive outcomes, in terms of physical and mental health and ability. If we apply to adolescence and aging, perhaps one form of training that would be extremely deterministic of cognitive efficacy in older adults is the amount of focus training experienced.

Likewise, if we were to train indivduals on how to focus their mental thoughts, and improve them over time, might brain activity be modulated? And subsequently, might cognitive abilities be improved or preserved better with age?

A structural model of aging, brain and behavior

Possible working structural model that can be tested with measures of stimulus, behavior, neuro-functional, neuro-anatomical variables. The dynamic influences of age and "culture" can also be tested. Culture here refers to long-term experiences of any kind. More complex models can be postulated from this current framework by adding more factors, or measures, and by also constraining the specific weights and covariances. In the broadest sense, the weights and covariances are modeled linearly. However, certainly, non-linear functions can be imposed. The result of such impositions would be a neural network with non-linear activation functions.

Age and Culture Modulate Face, House Processing in Ventral Visual Areas

This is the powerpoint (hosted on Google Docs; leave comment if buggy) for the presentation of this research work given at a talk during the Society for Neuroscience Annual Meeting, Washington DC, 2009.

Press Release: Culture and Aging fMRI Study

Culture, Aging fMR-Adaptation press release in UIUC News Bureau.

http://www.news.uiuc.edu/news/07/0501culture.html

Culture, Age and Eye-Movements

We repeated the same experiment as in the culture and aging adaptation fMRI study. Only this time, we were recording subject eye-movements. We know that there were already cultural differences in old adults in terms of brain activity. Specifically, old East Asian adults did not engage the object processing regions to the same degree as Old Westerners. But how do we really know for sure that this was related to visual processing and not some other form of cognitive operations at work. A way to understand this better was to use eye-tracking. Which is what mainly motivated this study. In parallel, this eye-tracking version of the paradigm allowed to examine three main questions:

1. Cultural experience with age predicts that individuals become more different as they become more developed in their culture (assuming that the cultures are different on some dimensions and levels). However, aging also leads to a phenomena called de-differentiation, which refers to the fact that cognitive processing in older adults becomes less individually distinct due to general decline and increased variability in performance. So it would seem these two forces are in opposition. Thus, one question was whether cultural difference diverge or converge with age.

2. Another question was whether these cultural differences are robust to environmental biases. Cultural biases are such that East Asians are context-oriented and Westerners are object-oriented. These are sweeping statements of course, and should in no way be understood as stereotypical. However, there is evidence that suggests that, for whatever reason, there are visual processing differences that are related to the cultural background of individuals, including this current study. The question though is if we were exposed to visual environments that biased us to attend to objects or backgrounds, how would we behave given our own cultural biases to one component over the other?

3. Finally, the last question is whether these cultural biases in visual processing is just an inconsequential behavior, or if it does indeed have impact on other cognitive processes, perhaps an obviously important process such as memory.

In sum, we found that cultural differences diverge with age, these cultural biases remain despite environmental biases, at least in a passive viewing case, and these biases also impact on memory such that the item we attend to less is subsequently less well remembered.

[CNS Poster 2007.pdf]

Cultural effects on visual processing as a function of age

Evidence shows that Westerners are more object-focused, being more individualistic, whereas East Asians are more context-focused, being more holistic. These differences are probably due to the larger historical cultural developmental influence exerted on individuals throughout their life experiences. Such influences permeate from the larger societal forces down to the everyday inter-relational communications, even to the physical habitational environment as an outward expression of these internal thoughts. With age, therefore, there is greater experience with one's own cultural development. We sought to examine these neural correlates of cultural experience with age.

The same study previously conducted with East Asians was conducted with Westerners. In summary, we found that Westerners showed similar object, background, and binding processing regions. These regions showed reduced expression with age. The most interesting contrast, however, was that Older East Asians did not show typical object processing (as measured using our adaptation paradigm; see subsequent follow-up experiments) while Young East Asians, Young Westerners and Old Westerners all showed object processing in the lateral occipital complex (LOC). This was related to changes in attentional resources with age. Furthermore, the difference was consistent with cultural expectations because the Old Westerners showed preserved object processing engagement, reflecting the more object-focused cultural background.

This study is currently in press in Cognitive, Affective, Behavioral Neuroscience journal. CNS 2006 abstract available for download.

So now, we know that differences in experiences over lifetime lead to differences in engagement of visual processing regions, and these differences are at the neural systems level as well. The next question how these patterns of neural engagement relate to what these people are actually looking at. This is important for understanding what is the actual visual information being attended. This has implications on developmental experience as a top-down modulator of the bottom-up visual information being input into higher cognitive processes. The other aspect is how external experience interacts with biological or cognitive changes related to aging.

What processes are specific to aging only? What processes are specific to long-term experience within the external developmental environment? Can short-term training alleviate processes that decline with age? What are the long-term experiences that lead to beneficial aging neural, cognitive outcomes?

This study had since had a press release [article].

Aging effects on visual object, background and binding processing

Earlier, we saw different brain regions involved in object, background and binding processing. Now, we see if these regions might be engaged differently in older adults. Older adults typically show poorer episodic memory but relatively preserved item processing that does not require episodic or contextual access. Might this be due to a reduced engagement of binding processes in the MTL of older adults?

We found that not only is MTL reduced, but older adults seemed to not process the entire visual stimuli in the same way as young adults. In particular, older adults seem to process only background components of the pictures while somewhat treating the objects less attentively. Abstract: Age-related changes in object processing and contextual binding revealed using fMR adaptation.

So we know that at least part of the changes in aging might be related to the partial processing of the entire picture rather than the entire central item and context. Next, we turn to consider what are some of the factors that might lead to these changes with age.

Binding information about items and their contexts

So we know frequency has bearing on how the brain works during semantic judgments, encoding, and retrieval. Now, we take a look more specifically at how the brain does the work of binding the item to information about its occurrence for subsequent memory. Previously, we showed that if you had to engage the brain more during encoding, you are more likely to remember the item's occurrence. Now, we are interested in where in the brain this occurrence information or contextual information about the item is processed.

We looked at pictures for this inquiry instead of words because they afforded more relevant ways of manipulating the stimuli, as well as the ability to test these items more easily in other sample groups of people as will become apparent later on.

When looking at pictures of objects in background scenes, we are able to process information about the identity of the object, the content or spatial layout of the background. Furthermore, we form the binding between object and background that relates to information about their co-occurrence. The brain regions involved in these respective processes are the lateral occipital complex (LOC), the parahippocampal place area (PPA), and the medial temporal regions (MTL) that includes a different region of the parahippocampal gyrus and the hippocampus. Abstract: Cortical areas involved in object, background, and object-background processing revealed with functional magnetic resonance adaptation.

Thus, we know that the brain processes the component item information and their contextual binding in seperate regions. These then give us clues about how these different regions might operate differently across people groups that show different memory behavior and/or processing of visual stimuli.