The Female Flipping Brain

The Neurocritic was perhaps a little harsh¹ on New Scientist in the previous post about The Female Macaque Brain. My complaints were with use of the words "gossip" and "gossipy" to describe the vocalizations of rhesus monkeys, and with mention of the stereotype "women are the chattier sex" without directly rebutting it.²

In the next New Scientist headline of the week,

Brain flip helps to relieve pre-menstrual stress

• 17:43 19 November 2008 by Ewen Callaway

The female brain has a clever way of mitigating the stress experienced during menstruation: it flip-flops.

The region of the brain used for coping with stress flips to the opposite side of the brain during a woman's period - from an area linked to negative emotion to one that usually deals with cheerier thoughts.

This story is so much better! Because we want to associate the female brain during menstruation with either waffling and indecision, or turning somersaults. But it seems like all this brain flipping is helpful:

Such a change could help women cope with the hormonal maelstrom going on in their bodies without causing huge behavioural shifts. Oestrogen levels levels, in particular, plummet around menstruation.

Now of course, the use of hyperbolic language to describe a change in the relative hemispheric asymmetry of MEG activity in prefrontal cortex is in no way designed to draw readers to what might otherwise be an esoteric research finding.³


OK. So the actual paper (Hwang et al., 2008b) expanded upon an earlier body of work suggesting that the left and right prefrontal cortices are part of separate neural systems involved in approach- and withdrawal-related emotions, respectively (Davidson et al., 2000). This view was initially based on brain lesion studies, with more recent evidence coming from electroencephalographic recordings. Broadly speaking, strokes and other injuries to the left frontal lobe more often lead to depression, because one of the regions associated with positive emotions is no longer intact. Conversely, damage to the right frontal lobe can lead to anosognosia, or denial of impairment, because a region associated with negative emotions is no longer intact. In the EEG realm, the evidence consists of frontal asymmetries in activity during positive and negative states. Spectral power in the alpha frequency band (8-12 Hz) is used as a measure of cortical activation, with reduced alpha power associated with greater activation. Although the evidence isn't entirely clear on this point, a baseline L>R frontal EEG asymmetry has been associated with a better coping style in response to stress.

Here's where the studies of Hwang and colleagues enter the scene. An earlier paper (Hwang et al., 2008a) looked at resting baseline frontal MEG asymmetries in women during two points of the menstrual cycle: the peri-ovulatory (OV) and menstrual (MC) phases:

Difference in spontaneous frontal alpha asymmetry pattern across the menstrual cycle was also noted. Relatively higher right frontal activity was found during the OV phase; relatively higher left frontal activity was noted during the MC phase. The alteration of frontal alpha asymmetry might serve a sub-clinical correlate for hormonal modulation effect on dynamic brain organization for the predisposition and conceptualization of different affective styles across the menstrual cycle.

This result seems counter-intuitive initially, because higher levels of estrogen (as during OV) are thought to increase approach behaviors and motivations, which would presumably be associated with greater left than right frontal activity. Contrary to this, the authors speculated that during MC, the relatively greater left-sided "happy" frontal activity is acting in a top-down fashion to dampen negative rumblings in the amygdala (although there is no absolutely no evidence for this). At both time points, the participants filled out questionnaires to asses state anxiety and approach/avoidance behaviors. Since the scores did not differ between the OV and MC phases, the authors suggested that the L>R frontal activity during MC was serving a useful purpose: to keep all those negative emotions in check. Note that none of the women in this study suffered from PMS. It would be important for their interpretation to test women with PMS and show that they do not have the L>R asymmetry during MC.

But let's look at the actual data. Basically, there was no asymmetry during OV, but greater R frontal activity during OV than MC [higher alpha = less activation].



Fig. 2 (Hwang et al., 2008a). The mean alpha power in the frontal regions at MC and OV phase. No [main] effect of hemispheric side and menstrual phase was noted. The phase by side analysis reveals a significant interaction (p = 0.004). Error bar represents the standard error of the mean. MEG alpha power is negatively related to the system activity.

Hmm.

Our results demonstrated that young females can express relatively greater resting right frontal activity during the OV as compared to MC phase. ... Estrogen has also been proposed to modulate the ‘arousal crescent’ of neurons in the female brain, improving assessment of the environment, threat anticipation, and preparing the organism for the stressful but ultimate goal of reproduction. It is contentious to speculate that higher right frontal activity could be a central correlate for achieving a higher readiness for fertility window.

It seems a little convoluted to postulate that greater activity in the so-called "withdrawal" system leads to a greater desire to mate.

Anyway. The more recent study of Hwang et al. (2008b) looked at MEG activity during a task where the female participants responded to pictures of faces with neutral, happy, or sad expressions and withheld responding to faces with fearful expressions. Here they looked at MEG activity evoked by the fearful face stimuli (evoked responses), rather than resting baseline activity. Although we don't get to see what the MEG data look like, results indicated that

the menstrual cycle was coupled with a shift of asymmetric lateralization of frontal activation across different menstrual phases. Evoked magnetic field activity in the time window 200-300ms (M1) and 300-450ms (M2) after stimulus onset demonstrated significant interactions between hemispheric side and menstrual phase. The right hemispheric dominance in periovulatory phase (OV) changed to left hemispheric dominance in menstrual (MC) phase. Significant association between the anxiety score and the left PFC activation was particularly observed in MC phase.

So in this study, there was a positive correlation between mean peak amplitude [thought to be a direct measure of activation] in the left PFC and state anxiety. Does this mean there's a failed attempt to regulate negative emotional responses to the fearful faces? It's not clear.

The take-home message?

It is conceivable to speculate that the dynamic change of left-right hemispheric preponderance may mediate automatic modulation and the emotional regulation across the menstrual cycle.

And thus ends the tale of the Female Flipping Brain on not a bang, but a whimper.

Footnote

¹ But then again, I'm not very good at seeing and understanding the needs of other people, so I might come across as arrogant, impatient and insensitive to people that need some time to understand what I am talking about.

² Much worse on this front was an article in The Scotsman, Why do women chat more than men? Macaque monkeys could hold the answers.

³ One of these days I'll stop reading press releases and popular science coverage...but then again, what would I write about?

References

Davidson RJ, Jackson DC, Kalin NH. (2000). Emotion, plasticity, context, and regulation: perspectives from affective neuroscience. Psychol Bull. 126:890-909.

R HWANG, L CHEN, T YEH, P TU, C TU, J HSIEH (2008a). The resting frontal alpha asymmetry across the menstrual cycle: A magnetoencephalographic study. Hormones and Behavior, 54 (1), 28-33 DOI: 10.1016/j.yhbeh.2007.11.007

Ren-Jen Hwang, Chi-Hsun Wu, Li-Fen Chen, Tzu-Chen Yeh, Jen-Chuen Hsieh (2008b). Female menstrual phases modulate human prefrontal asymmetry: A magnetoencephalographic study. Hormones and Behavior. Nov 1. [Epub ahead of print].

We previously reported that the trait/baseline prefrontal cortex (PFC) activity expresses a dynamic plasticity during female menstrual cycle. The shift of asymmetric lateralization of PFC baseline activity pinpoints a possible emotional regulation of negative affection. The current emotional Go/NoGo study aimed to investigate the state PFC responses of different menstrual phases during fear facial stimulation in fourteen healthy women. Our data disclosed that the menstrual cycle was coupled with a shift of asymmetric lateralization of frontal activation across different menstrual phases. Evoked magnetic field activity in the time window 200-300 ms (M1) and 300-450 ms (M2) after stimulus onset demonstrated significant interactions between hemispheric side and menstrual phase. The right hemispheric dominance in periovulatory phase (OV) changed to left hemispheric dominance in menstrual (MC) phase. Significant association between the anxiety score and the left PFC activation was particularly observed in MC phase. Our study revealed a plastic resilience of functional organization of human brain and a dynamic automaticity of inter-hemispheric synergism for possible adaptive regulation under the aversive confrontation in accordance with hormonal fluctuation during the menstrual cycle.