Neurology -- Correspondence for Cappa et al., 59 (5) 720-723

Correspondence published:

Reply to Letter to the Editor: C Miniussi, S F Cappa, M Sandrini, P M Rossini and K Sosta (29 October 2002)

The role of the left frontal lobe in action naming: rTMS evidence: Agnes Floeel, Stefan Knecht (29 October 2002)

Reply to Letter to the Editor 29 October 2002

C Miniussi
IRCCS Italy,
S F Cappa, M Sandrini, P M Rossini and K Sosta
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Re: Reply to Letter to the Editor

neuro_journal{at}urmc.rochester.edu C Miniussi, et al.

Flöel et al. correctly point out that in two experiments, involving, respectively, memory for complex pictures [5], and picture naming [2], we obtained two apparently contrasting results using the same stimulation measurements. In the case of memory, we reported an increase in the number of errors with frontal stimulation, while naming was actually "facilitated" (i.e. response latency was reduced) with comparable stimulation. We fully agree that these results underline the complexity of the effects of rTMS on behavioural performance; in particular, they highlight the importance of an accurate task analysis. Encoding and retrieval of novel, non-verbal information is hardly comparable to the naming of familiar pictures; as discussed in our paper, [2] the puzzling result of naming facilitation has already been reported. [6, 7, 8]
However, the basis for these effects of rTMS on behaviour remains essentially unknown and variability in response between subjects has been demonstrated only for corticospinal excitability. [4] An (admittedly speculative) interpretation of this finding is that the process of lexical selection may be facilitated by an inhibition of competitors of the target, as suggested by some word production models. [9] Nevertheless, we agree that more experimentation is required before considering the possibility that these facilitatory TMS effects may have implications for treatment strategies in aphasic patients.
References:
1. Boroojerdi B, Phipps M, Kopylev L, Wharton CM, Cohen LG, Grafman J. Enhancing analogic reasoning with rTMS over the left prefrontal cortex. Neurology 2001;56:526-528.
2. Cappa SF, Sandrini M, Rossini PM, Sosta K, Miniussi C. The role of the left frontal lobe in action naming—rTMs evidence. Neurology 2002;59:720-723.
3. Harmer CJ, Thilo KV, Rothwell JC, Goodwin GM. Transcranial magnetic stimulation of medial-frontal cortex impairs the processing of angry facial expressions. Nat. Neurosci 2001;4:17-18.
4. Maeda F, Keenan JP, Tormos JM, Topka H, Pascual-Leone A. Interindividual variability of the modulatory effects of repetitive transcranial magnetic stimulation on cortical excitability. Exp Brain Res 2000;133:425-430.
5. Rossi S, Cappa SF, Babiloni C, Pasqualetti P, Miniussi C, Carducci F, Babiloni F, Rossini PM. Prefontal cortex in long-term memory: an "interference" approach using magnetic stimulation. Nat Neurosci 2001;4:948-952.
6. Mottaghy FM, Hugs M, Brugmann M. et al. Facilitation of picture naming after repetetive transcranial magnetic stimulation. Neurology 1999;53:1806-1812.
7. Topper R, Mottaghy F, Brugmann M, Noth J, Huber W. Facilitation of picture naming by focal transcranial magnetic stimulation of Wernicke’s area. Exp. Brain Res. 1998;121:371-378.
8. Sparing R, Mottaghy FM, Hungs M, Brugmann M, Foltys H, Huber W, Topper. R.Repetetive transcranial magnetic stimulation effects on language function depend on the stimulation parameters. J Clin Neurophysiol; 2001;18:326-330.
9. Dell GS, O'Seaghdha PG. Stages of lexical access in language production. Cognition 1992;42:287-314.

The role of the left frontal lobe in action naming: rTMS evidence 29 October 2002

Agnes Floeel
University of Muenster Germany,
Stefan Knecht
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Re: The role of the left frontal lobe in action naming: rTMS evidence

floeel{at}uni-muenster.de Agnes Floeel, et al.

We read with great interest the article by Cappa et al. [2] on the role of the left frontal lobe in action naming. The authors demonstrated facilitation of action naming through application of 20 Hz subthreshold rTMS (90% of resting motor threshold [rMT]) for 500 msec duration, applied over left prefrontal cortex. The demonstration of facilitatory TMS effects is highly warranted because of the potential implication for therapeutic strategies in brain-damaged patients.
We are not sure though how consistent and therefore replicable the effects are. The same group recently published a report demonstrating inhibition of verbal cognitive functions after TMS over left (for encoding) and right (for retrieval) dorsolateral prefrontal cortex. [5] The TMS measurements were identical (500 ms, 20 Hz, 90% of rMT) to the ones used in their recent work.
There are additional reports on facilitation of verbal cognitive functions, in this case analogic reasoning, with high-frequency subthreshold rTMS over the left prefrontal cortex. [1] Stimulation intensity and frequency were, however, lower (5 Hz, 90% of active MT, three trains of 10-s duration each). The reverse effect, i.e., inhibition by rTMS over medial prefrontal cortex has also been demonstrated using high-frequency rTMS, although at a higher intensity (10 Hz for 500 msec, 110% of rMT; processing of angry facial expressions). [3]
Although rTMS effects of a given frequency have been shown to vary between subjects—measurements that are inhibitory in one subject might be facilitatory in the next —, [4] the diametrical effects of rTMS over prefrontal cortex during verbal processing are surprising and require further explanation. [2, 5]
References:
1. Boroojerdi B, Phipps M, Kopylev L, Wharton CM, Cohen LG, Grafman J. Enhancing analogic reasoning with rTMS over the left prefrontal cortex. Neurology 2001;56:526-528.
2. Cappa SF, Sandrini M, Rossini PM, Sosta K, Miniussi C. The role of the left frontal lobe in action naming—rTMs evidence. Neurology 2002;59:720-723.
3. Harmer CJ, Thilo KV, Rothwell JC, Goodwin GM. Transcranial magnetic stimulation of medial-frontal cortex impairs the processing of angry facial expressions. Nat. Neurosci 2001;4:17-18.
4. Maeda F, Keenan JP, Tormos JM, Topka H, Pascual-Leone A. Interindividual variability of the modulatory effects of repetitive transcranial magnetic stimulation on cortical excitability. Exp Brain Res 2000;133:425-430.
5. Rossi S, Cappa SF, Babiloni C, Pasqualetti P, Miniassi C, Carducci F, Babiloni F, Rossigni PM. Prefontal cortex in long-term memory: an "interference" approach using magnetic stimulation. Nat Neurosci 2001;4:948-952.