Monday, September 22, 2014

"Single Dose of Antidepressant Changes the Brain" - The Trouble with Ignorant Science Writers

"Single Dose of Antidepressant Changes the Brain," that was the headline from Science Codex on Thursday, and their headline resembled a lot of others, as well. Here are some other examples, from Time Magazine, "One Dose of Antidepressant Changes the Brain, Study Finds,"or from The Examiner, "SSRIs change brain structure fast," or from Psych Central, "Single Dose of Antidepressant Changes the Brain."

So, what't the problem with these headlines?

The issue is that the study never claimed that SSRIs change the brain (and especially not brain structure) but, rather, they found (as others have before them) that a single dose of an SSRI can alter functional connectivity in the brain.

For the purpose of clarity (via Wikipedia):
Functional connectivity is the connectivity between brain regions that share functional properties. More specifically, it can be defined as the temporal correlation between spatially remote neurophysiological events, expressed as deviation from statistical independence across these events in distributed neuronal groups and areas.
Functional connectivity is dynamic, which means it can change at the order of seconds in response to stimuli of various types.

What the study actually found is that an SSRI (Lexapro in this study) reduces the level of intrinsic connectivity in most parts of the brain, while it increases connectivity within two brain regions, specifically the cerebellum and thalamus. From Laird, et al (2013):
The term “intrinsic connectivity network” (Seeley et al., 2007), therefore, expands upon the concept of resting state networks to include the set of large-scale functionally connected brain networks that can be captured in either resting state or task-based neuroimaging data.
From Wikipedia:
The cerebellum (Latin for "little brain") is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses;[1] its movement-related functions are the most solidly established. The cerebellum does not initiate movement, but it contributes to coordination, precision, and accurate timing. It receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine tune motor activity.[2]
The thalamus has multiple functions. It may be thought of as a kind of switchboard of information. It is generally believed to act as a relay between different subcortical areas and the cerebral cortex. In particular, every sensory system (with the exception of the olfactory system) includes a thalamic nucleus that receives sensory signals and sends them to the associated primary cortical area. For the visual system, for example, inputs from the retina are sent to the lateral geniculate nucleus of the thalamus, which in turn projects to the visual cortex in the occipital lobe. The thalamus is believed to both process sensory information as well as relay it—each of the primary sensory relay areas receives strong feedback connections from the cerebral cortex. Similarly the medial geniculate nucleus acts as a key auditory relay between the inferior colliculus of the midbrain and the primary auditory cortex, and the ventral posterior nucleus is a key somatosensory relay, which sends touch and proprioceptive information to the primary somatosensory cortex.

The thalamus also plays an important role in regulating states of sleep and wakefulness.[10] Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming thalamo-cortico-thalamic circuits that are believed to be involved with consciousness. The thalamus plays a major role in regulating arousal, the level of awareness, and activity. Damage to the thalamus can lead to permanent coma.

The role of the thalamus in the more anterior pallidal and nigral territories in the basal ganglia system disturbances is recognized but still poorly understood. The contribution of the thalamus to vestibular or to tectal functions is almost ignored. The thalamus has been thought of as a "relay" that simply forwards signals to the cerebral cortex. Newer research suggests that thalamic function is more selective.[11] Many different functions are linked to various regions of the thalamus. This is the case for many of the sensory systems (except for the olfactory system), such as the auditory, somatic, visceral, gustatory and visual systems where localized lesions provoke specific sensory deficits. A major role of the thalamus is devoted to "motor" systems. The thalamus is functionally connected to the hippocampus [12] as part of the extended hippocampal system at the thalamic anterior nuclei[13] with respect to spatial memory and spatial sensory datum they are crucial for human episodic memory and rodent event memory.[14][15] There is support for the hypothesis that thalamic regions connection to particular parts of the mesio-temporal lobe provide differentiation of the functioning of recollective and familiarity memory.[9]

The neuronal information processes necessary for motor control were proposed as a network involving the thalamus as a subcortical motor centre.[16] Through investigations of the anatomy of the brains of primates[17] the nature of the interconnected tissues of the cerebellum to the multiple motor cortices suggested that the thalamus fulfills a key function in providing the specific channels from the basal ganglia and cerebellum to the cortical motor areas.[18][19] In an investigation of the saccade and antisaccade[20] motor response in three monkeys, the thalamic regions were found to be involved in the generation of antisaccade eye-movement.[21]
It's unclear how these structures are involved in depression, although the thalamus is connected to the hypothalamus, which is impacted by trauma (since it plays a role in memory) and which may play a role in depression due to its function in memory and emotional processing.

Based on all of this it is clear that the study in question was greatly simplified in the press releases and media coverage.

For a more educated takedown of the press coverage of this study, Neuroskeptic has written a great post.

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