Notes for Tokyo lecture given 11/27/18. This is too complex for me, much less an audience, so I simplified it. Robert D. McMullen, MD (only I have pswd to signature)
THE MAIN THREE NETWORKS OF THE BRAIN ARE: SN (salience network): the network focused on here
DMN (default mode network) –self-referential; it is activated during social reasoning, such as when we think about our own and/or others’ minds. signals from AI influence DMN;
CEN (central executive network) – key nodes in PPC (Posterior parietal cortex); maintenance and manipulation of information and decision-making ;
OTHER, SMALLER, NETWORKS: Cinguloopercular network -set-maintenance activities
Ventral attention network –right lateralized ; overlaps with SN
Task Positive Network (TPN): activated by mechanical, causal, logical, or mathematical reasoning—e.g., when watching videos about physics
SALIENCE NETWORK (SN)
etymology: Salient: from leaping in Latin, used for a military bulge; something protruding, standing out.
Salience: being noticeable, standing out. Salient entities attract attention, are meaningful or behaviorally relevant—e.g., something out of the ordinary occurring; wrestling with an important question—e.g., a moral question, a decision about what job to take. (Salience detection has been most studied in visual research.)
- low-level sensory features (e.g., stimulus color or intensity—usually an abrupt change in these)
- high-level cognitive and affective processes (e.g., emotional salience or personal relevance).
The SN PLAYS A CENTRAL ROLE IN COGNITIVE CONTROL (Sarah Peters, Downar)
- integrating sensory input to guide attention; attend to motivationally salient stimuli
- recruit appropriate functional brain-behavior networks to modulate behavior.
ABNORMAL STRUCTURE AND FUNCTION are especially significant in the TWO MAJOR CORTICAL NODES OF THE SN:
1—dorsal anterior cingulate cortex (dACC) 2—anterior insula (AI)
ASSOCIATED SUBCORTICAL STRUCTURES IN THE SN INCLUDE:
3—dorsal striatum 4—mediodorsal thalamus 5–dopaminergic brainstem nuclei
The above five SN structures comprise a discrete regulatory loop circuit—the cortico-striato-thalamocortical loop of the SN. This loop is central to mechanisms of cognitive control. SN dysfunction impairs self-regulation of cognition, behavior, and emotion. All psychiatric disorders include loss of cognitive control, which is clearly manifested by distortions of perception. E.g., a person with panic attacks has an excessive fear of the world and the future, even if they recognize their continual anxiety is making them irrational.
The only patient who never responds to TMS is someone with Major Depressive Disorder (MDD) who has no cognitive distortions. They do not have low self-esteem or excessive guilt. They do not blame themselves They do not view others or the world negatively. They know they have an illness. They regret they do not function and regret that others must help them. It is possible these people have no dysfunction in the SN, but I do not think Dr Downar has studied them yet since they are so uncommon. I had one, a 22 y.o. with lifelong severe depression, who did not respond at all to over 75 TMS treatments.]
Abnormalities in the SN occur in MDD, SUD (Substance Use Disorder), anxiety disorders, OCD, schizophrenia, and ED’s (eating disorders).
A common substrate across all diagnoses is loss of gray matter in the dACC (dorsal anterior cingulate cortex) and bilateral AI (anterior insula). The loci of gray matter loss corresponded closely with the core cortical nodes of the SN. The resultant impairment of cognitive control is a transdiagnostic feature across many psychiatric illnesses (McTeague et al., 2016) and a target for brain stimulation (Downar et al.,2016).
- rTMS normalizes abnormalities in the SN loop. This may be why TMS occasionally puts multiple chronic disorders into complete remission in a single person—an outcome that is unimaginable even with multiple medications. I have 3 to 4 patients with such surprising outcomes, which I will soon describe to you.
Addendums, with some additional details
- Examples of patients with multiple psychiatric diagnoses who became completely normal with TMS. One would scarcely imagine this outcome.
- Description of successful TMS treatment of bipolar depression and how to do it safely.
- Y.I.: Our OCD results with TMS using Brainsway h7 helmet:
Five out of 20 [25%] of our patients had a greater than 50% decline in the YBOCS . The average decline was 69%. The average number of treatments was 34.
Six out of 20 [30%] had 25-50% decline in YBOCS—an average of 36, average treatments 55.
So 55% of 20 patients had a >25% decline in YBOCS, with an average 51% decline in YBOCS and an average of 45 TMS treatments